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 $221.60   11.400%   $246.8624   $246.86   $246.85   $246.90  
  Purchase #2 $45.99   6.426%   $48.9453   $48.95   $48.95   $48.90  
  Purchase #3 $215.31   13.632%   $244.6611   $244.66   $244.65   $244.70  
  Purchase #4 $121.29   3.665%   $125.7353   $125.74   $125.75   $125.70  
  Purchase #5 $225.32   11.590%   $251.4346   $251.43   $251.45   $251.40  
  Purchase #6 $75.67   3.201%   $78.0922   $78.09   $78.10   $78.10  
  Purchase #7 $23.66   12.103%   $26.5236   $26.52   $26.50   $26.50  
  7 purchase totals = $928.84       $1,022.2545   $1,022.25   $1,022.25   $1,022.20