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 $76.74   5.800%   $81.1909   $81.19   $81.20   $81.20  
  Purchase #2 $141.47   10.597%   $156.4616   $156.46   $156.45   $156.50  
  Purchase #3 $219.42   7.801%   $236.537   $236.54   $236.55   $236.50  
  Purchase #4 $46.94   9.867%   $51.5716   $51.57   $51.55   $51.60  
  Purchase #5 $166.29   10.625%   $183.9583   $183.96   $183.95   $184.00  
  Purchase #6 $247.77   4.858%   $259.8067   $259.81   $259.80   $259.80  
  Purchase #7 $61.72   4.843%   $64.7091   $64.71   $64.70   $64.70  
  7 purchase totals = $960.35       $1,034.2352   $1,034.24   $1,034.20   $1,034.30