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 $48.94   9.263%   $53.4733   $53.47   $53.45   $53.50  
  Purchase #2 $213.85   8.783%   $232.6324   $232.63   $232.65   $232.60  
  Purchase #3 $192.49   4.742%   $201.6179   $201.62   $201.60   $201.60  
  Purchase #4 $57.84   7.586%   $62.2277   $62.23   $62.25   $62.20  
  Purchase #5 $215.64   3.314%   $222.7863   $222.79   $222.80   $222.80  
  Purchase #6 $31.60   8.764%   $34.3694   $34.37   $34.35   $34.40  
  Purchase #7 $67.39   5.252%   $70.9293   $70.93   $70.95   $70.90  
  7 purchase totals = $827.75       $878.0363   $878.04   $878.05   $878.00