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 $171.29   8.786%   $186.3395   $186.34   $186.35   $186.30  
  Purchase #2 $97.62   10.647%   $108.0136   $108.01   $108.00   $108.00  
  Purchase #3 $156.98   9.410%   $171.7518   $171.75   $171.75   $171.80  
  Purchase #4 $225.86   8.437%   $244.9158   $244.92   $244.90   $244.90  
  Purchase #5 $69.91   6.712%   $74.6024   $74.60   $74.60   $74.60  
  Purchase #6 $180.56   5.436%   $190.3752   $190.38   $190.40   $190.40  
  Purchase #7 $235.82   6.414%   $250.9455   $250.95   $250.95   $250.90  
  7 purchase totals = $1,138.04       $1,226.9438   $1,226.95   $1,226.95   $1,226.90