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 $83.40   11.473%   $92.9685   $92.97   $92.95   $93.00  
  Purchase #2 $238.40   5.432%   $251.3499   $251.35   $251.35   $251.30  
  Purchase #3 $157.30   5.515%   $165.9751   $165.98   $166.00   $166.00  
  Purchase #4 $47.34   11.467%   $52.7685   $52.77   $52.75   $52.80  
  Purchase #5 $127.79   8.303%   $138.4004   $138.40   $138.40   $138.40  
  Purchase #6 $163.67   12.267%   $183.7474   $183.75   $183.75   $183.70  
  Purchase #7 $148.48   5.478%   $156.6137   $156.61   $156.60   $156.60  
  7 purchase totals = $966.38       $1,041.8235   $1,041.83   $1,041.80   $1,041.80