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 $98.60   11.701%   $110.1372   $110.14   $110.15   $110.10  
  Purchase #2 $162.82   8.620%   $176.8551   $176.86   $176.85   $176.90  
  Purchase #3 $35.84   12.127%   $40.1863   $40.19   $40.20   $40.20  
  Purchase #4 $119.72   6.484%   $127.4826   $127.48   $127.50   $127.50  
  Purchase #5 $121.71   13.390%   $138.007   $138.01   $138.00   $138.00  
  Purchase #6 $31.43   9.277%   $34.3458   $34.35   $34.35   $34.30  
  Purchase #7 $178.33   11.640%   $199.0876   $199.09   $199.10   $199.10  
  7 purchase totals = $748.45       $826.1016   $826.12   $826.15   $826.10