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 $193.63   12.165%   $217.1851   $217.19   $217.20   $217.20  
  Purchase #2 $88.83   3.520%   $91.9568   $91.96   $91.95   $92.00  
  Purchase #3 $93.30   5.421%   $98.3578   $98.36   $98.35   $98.40  
  Purchase #4 $169.99   7.764%   $183.188   $183.19   $183.20   $183.20  
  Purchase #5 $71.66   5.102%   $75.3161   $75.32   $75.30   $75.30  
  Purchase #6 $162.67   13.800%   $185.1185   $185.12   $185.10   $185.10  
  Purchase #7 $206.79   6.586%   $220.4092   $220.41   $220.40   $220.40  
  7 purchase totals = $986.87       $1,071.5315   $1,071.55   $1,071.50   $1,071.60