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 $119.67   5.435%   $126.1741   $126.17   $126.15   $126.20  
  Purchase #2 $93.91   5.718%   $99.2798   $99.28   $99.30   $99.30  
  Purchase #3 $70.94   9.409%   $77.6147   $77.61   $77.60   $77.60  
  Purchase #4 $219.56   12.582%   $247.185   $247.19   $247.20   $247.20  
  Purchase #5 $168.80   7.847%   $182.0457   $182.05   $182.05   $182.00  
  Purchase #6 $48.43   11.591%   $54.0435   $54.04   $54.05   $54.00  
  Purchase #7 $87.94   3.225%   $90.7761   $90.78   $90.80   $90.80  
  7 purchase totals = $809.25       $877.1189   $877.12   $877.15   $877.10