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 $127.68   13.122%   $144.4342   $144.43   $144.45   $144.40  
  Purchase #2 $59.29   4.852%   $62.1668   $62.17   $62.15   $62.20  
  Purchase #3 $27.31   4.354%   $28.4991   $28.50   $28.50   $28.50  
  Purchase #4 $186.39   8.842%   $202.8706   $202.87   $202.85   $202.90  
  Purchase #5 $194.78   9.404%   $213.0971   $213.10   $213.10   $213.10  
  Purchase #6 $209.51   12.324%   $235.33   $235.33   $235.35   $235.30  
  Purchase #7 $173.93   10.742%   $192.6136   $192.61   $192.60   $192.60  
  7 purchase totals = $978.89       $1,079.0114   $1,079.01   $1,079.00   $1,079.00