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 $52.85   8.478%   $57.3306   $57.33   $57.35   $57.30  
  Purchase #2 $158.55   7.849%   $170.9946   $170.99   $171.00   $171.00  
  Purchase #3 $234.34   8.731%   $254.8002   $254.80   $254.80   $254.80  
  Purchase #4 $113.91   7.154%   $122.0591   $122.06   $122.05   $122.10  
  Purchase #5 $61.97   8.239%   $67.0757   $67.08   $67.10   $67.10  
  Purchase #6 $79.68   7.204%   $85.4201   $85.42   $85.40   $85.40  
  Purchase #7 $182.95   9.489%   $200.3101   $200.31   $200.30   $200.30  
  7 purchase totals = $884.25       $957.9904   $957.99   $958.00   $958.00