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 $15.75   4.606%   $16.4754   $16.48   $16.50   $16.50  
  Purchase #2 $100.80   5.181%   $106.0224   $106.02   $106.00   $106.00  
  Purchase #3 $221.86   6.215%   $235.6486   $235.65   $235.65   $235.60  
  Purchase #4 $223.32   11.525%   $249.0576   $249.06   $249.05   $249.10  
  Purchase #5 $35.35   11.748%   $39.5029   $39.50   $39.50   $39.50  
  Purchase #6 $99.52   3.684%   $103.1863   $103.19   $103.20   $103.20  
  Purchase #7 $138.81   6.306%   $147.5634   $147.56   $147.55   $147.60  
  7 purchase totals = $835.41       $897.4566   $897.46   $897.45   $897.50