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 $134.54   5.553%   $142.011   $142.01   $142.00   $142.00  
  Purchase #2 $139.94   12.125%   $156.9077   $156.91   $156.90   $156.90  
  Purchase #3 $69.95   8.303%   $75.7579   $75.76   $75.75   $75.80  
  Purchase #4 $97.75   13.363%   $110.8123   $110.81   $110.80   $110.80  
  Purchase #5 $229.80   12.678%   $258.934   $258.93   $258.95   $258.90  
  Purchase #6 $133.81   10.171%   $147.4198   $147.42   $147.40   $147.40  
  Purchase #7 $147.73   8.496%   $160.2811   $160.28   $160.30   $160.30  
  7 purchase totals = $953.52       $1,052.1238   $1,052.12   $1,052.10   $1,052.10