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 $147.84   5.591%   $156.1057   $156.11   $156.10   $156.10  
  Purchase #2 $216.93   13.600%   $246.4325   $246.43   $246.45   $246.40  
  Purchase #3 $54.42   13.462%   $61.746   $61.75   $61.75   $61.70  
  Purchase #4 $182.28   10.807%   $201.979   $201.98   $202.00   $202.00  
  Purchase #5 $207.34   9.151%   $226.3137   $226.31   $226.30   $226.30  
  Purchase #6 $231.79   5.649%   $244.8838   $244.88   $244.90   $244.90  
  Purchase #7 $248.38   4.743%   $260.1607   $260.16   $260.15   $260.20  
  7 purchase totals = $1,288.98       $1,397.6214   $1,397.62   $1,397.65   $1,397.60