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 $54.59   6.161%   $57.9533   $57.95   $57.95   $58.00  
  Purchase #2 $232.92   12.772%   $262.6685   $262.67   $262.65   $262.70  
  Purchase #3 $154.34   5.293%   $162.5092   $162.51   $162.50   $162.50  
  Purchase #4 $188.25   7.670%   $202.6888   $202.69   $202.70   $202.70  
  Purchase #5 $169.92   10.211%   $187.2705   $187.27   $187.25   $187.30  
  Purchase #6 $174.90   9.451%   $191.4298   $191.43   $191.45   $191.40  
  Purchase #7 $235.79   6.867%   $251.9817   $251.98   $252.00   $252.00  
  7 purchase totals = $1,210.71       $1,316.5018   $1,316.50   $1,316.50   $1,316.60