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 $108.97   4.656%   $114.0436   $114.04   $114.05   $114.00  
  Purchase #2 $14.56   12.196%   $16.3357   $16.34   $16.35   $16.30  
  Purchase #3 $55.36   12.334%   $62.1881   $62.19   $62.20   $62.20  
  Purchase #4 $148.99   13.426%   $168.9934   $168.99   $169.00   $169.00  
  Purchase #5 $205.35   13.104%   $232.2591   $232.26   $232.25   $232.30  
  Purchase #6 $220.85   6.831%   $235.9363   $235.94   $235.95   $235.90  
  Purchase #7 $84.68   4.328%   $88.345   $88.35   $88.35   $88.30  
  7 purchase totals = $838.76       $918.1012   $918.11   $918.15   $918.00