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 $44.83   10.410%   $49.4968   $49.50   $49.50   $49.50  
  Purchase #2 $169.86   12.810%   $191.6191   $191.62   $191.60   $191.60  
  Purchase #3 $116.57   4.351%   $121.642   $121.64   $121.65   $121.60  
  Purchase #4 $148.32   3.646%   $153.7277   $153.73   $153.75   $153.70  
  Purchase #5 $182.71   10.765%   $202.3787   $202.38   $202.40   $202.40  
  Purchase #6 $153.79   13.733%   $174.91   $174.91   $174.90   $174.90  
  Purchase #7 $235.58   7.395%   $253.0011   $253.00   $253.00   $253.00  
  7 purchase totals = $1,051.66       $1,146.7754   $1,146.78   $1,146.80   $1,146.70