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 $92.50   13.111%   $104.6277   $104.63   $104.65   $104.60  
  Purchase #2 $192.45   13.276%   $217.9997   $218.00   $218.00   $218.00  
  Purchase #3 $109.56   11.297%   $121.937   $121.94   $121.95   $121.90  
  Purchase #4 $23.58   6.137%   $25.0271   $25.03   $25.05   $25.00  
  Purchase #5 $54.39   4.133%   $56.6379   $56.64   $56.65   $56.60  
  Purchase #6 $49.34   3.791%   $51.2105   $51.21   $51.20   $51.20  
  Purchase #7 $184.73   5.774%   $195.3963   $195.40   $195.40   $195.40  
  7 purchase totals = $706.55       $772.8362   $772.85   $772.90   $772.70