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 $203.86   13.792%   $231.9764   $231.98   $232.00   $232.00  
  Purchase #2 $203.42   3.398%   $210.3322   $210.33   $210.35   $210.30  
  Purchase #3 $62.39   10.210%   $68.76   $68.76   $68.75   $68.80  
  Purchase #4 $180.53   11.868%   $201.9553   $201.96   $201.95   $202.00  
  Purchase #5 $173.31   10.259%   $191.0899   $191.09   $191.10   $191.10  
  Purchase #6 $30.93   6.731%   $33.0119   $33.01   $33.00   $33.00  
  Purchase #7 $175.63   6.593%   $187.2093   $187.21   $187.20   $187.20  
  7 purchase totals = $1,030.07       $1,124.3350   $1,124.34   $1,124.35   $1,124.40