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 $9.85   12.242%   $11.0558   $11.06   $11.05   $11.10  
  Purchase #2 $142.59   7.432%   $153.1873   $153.19   $153.20   $153.20  
  Purchase #3 $116.44   12.132%   $130.5665   $130.57   $130.55   $130.60  
  Purchase #4 $209.75   12.297%   $235.543   $235.54   $235.55   $235.50  
  Purchase #5 $43.75   8.519%   $47.4771   $47.48   $47.50   $47.50  
  Purchase #6 $44.30   3.821%   $45.9927   $45.99   $46.00   $46.00  
  Purchase #7 $240.70   5.516%   $253.977   $253.98   $254.00   $254.00  
  7 purchase totals = $807.38       $877.7994   $877.81   $877.85   $877.90