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 $227.51   6.318%   $241.8841   $241.88   $241.90   $241.90  
  Purchase #2 $24.85   13.484%   $28.2008   $28.20   $28.20   $28.20  
  Purchase #3 $81.34   13.245%   $92.1135   $92.11   $92.10   $92.10  
  Purchase #4 $111.89   12.107%   $125.4365   $125.44   $125.45   $125.40  
  Purchase #5 $33.29   3.823%   $34.5627   $34.56   $34.55   $34.60  
  Purchase #6 $23.77   8.546%   $25.8014   $25.80   $25.80   $25.80  
  Purchase #7 $209.96   9.369%   $229.6312   $229.63   $229.65   $229.60  
  7 purchase totals = $712.61       $777.6302   $777.62   $777.65   $777.60