Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $194.79   9.791%   $213.8619   $213.86   $213.85   $213.90  
  Purchase #2 $110.34   11.316%   $122.8261   $122.83   $122.85   $122.80  
  Purchase #3 $197.83   10.318%   $218.2421   $218.24   $218.25   $218.20  
  Purchase #4 $249.83   6.111%   $265.0971   $265.10   $265.10   $265.10  
  Purchase #5 $206.70   13.671%   $234.958   $234.96   $234.95   $235.00  
  Purchase #6 $230.50   5.544%   $243.2789   $243.28   $243.30   $243.30  
  Purchase #7 $211.26   11.394%   $235.331   $235.33   $235.35   $235.30  
  7 purchase totals = $1,401.25       $1,533.5951   $1,533.60   $1,533.65   $1,533.60