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 $201.54   11.666%   $225.0517   $225.05   $225.05   $225.10  
  Purchase #2 $246.63   11.685%   $275.4487   $275.45   $275.45   $275.40  
  Purchase #3 $142.74   10.614%   $157.8904   $157.89   $157.90   $157.90  
  Purchase #4 $202.75   8.655%   $220.298   $220.30   $220.30   $220.30  
  Purchase #5 $164.72   5.869%   $174.3874   $174.39   $174.40   $174.40  
  Purchase #6 $190.34   9.281%   $208.0055   $208.01   $208.00   $208.00  
  Purchase #7 $38.31   8.151%   $41.4326   $41.43   $41.45   $41.40  
  7 purchase totals = $1,187.03       $1,302.5143   $1,302.52   $1,302.55   $1,302.50