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 $218.31   11.672%   $243.7911   $243.79   $243.80   $243.80  
  Purchase #2 $94.81   9.272%   $103.6008   $103.60   $103.60   $103.60  
  Purchase #3 $142.40   8.310%   $154.2334   $154.23   $154.25   $154.20  
  Purchase #4 $215.68   9.473%   $236.1114   $236.11   $236.10   $236.10  
  Purchase #5 $239.54   12.392%   $269.2238   $269.22   $269.20   $269.20  
  Purchase #6 $38.32   6.389%   $40.7683   $40.77   $40.75   $40.80  
  Purchase #7 $215.28   5.817%   $227.8028   $227.80   $227.80   $227.80  
  7 purchase totals = $1,164.34       $1,275.5316   $1,275.52   $1,275.50   $1,275.50