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 $62.55   6.217%   $66.4387   $66.44   $66.45   $66.40  
  Purchase #2 $88.33   7.218%   $94.7057   $94.71   $94.70   $94.70  
  Purchase #3 $24.97   4.719%   $26.1483   $26.15   $26.15   $26.10  
  Purchase #4 $164.28   3.336%   $169.7604   $169.76   $169.75   $169.80  
  Purchase #5 $219.48   11.700%   $245.1592   $245.16   $245.15   $245.20  
  Purchase #6 $250.88   11.434%   $279.5656   $279.57   $279.55   $279.60  
  Purchase #7 $108.25   10.819%   $119.9616   $119.96   $119.95   $120.00  
  7 purchase totals = $918.74       $1,001.7395   $1,001.75   $1,001.70   $1,001.80