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 $120.85   11.669%   $134.952   $134.95   $134.95   $135.00  
  Purchase #2 $155.43   7.597%   $167.238   $167.24   $167.25   $167.20  
  Purchase #3 $217.89   8.728%   $236.9074   $236.91   $236.90   $236.90  
  Purchase #4 $19.84   11.313%   $22.0845   $22.08   $22.10   $22.10  
  Purchase #5 $58.56   3.117%   $60.3853   $60.39   $60.40   $60.40  
  Purchase #6 $180.40   11.602%   $201.33   $201.33   $201.35   $201.30  
  Purchase #7 $184.83   13.480%   $209.7451   $209.75   $209.75   $209.70  
  7 purchase totals = $937.80       $1,032.6423   $1,032.65   $1,032.70   $1,032.60