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 $86.29   12.360%   $96.9554   $96.96   $96.95   $97.00  
  Purchase #2 $136.70   9.385%   $149.5293   $149.53   $149.55   $149.50  
  Purchase #3 $148.61   8.493%   $161.2314   $161.23   $161.25   $161.20  
  Purchase #4 $132.84   6.379%   $141.3139   $141.31   $141.30   $141.30  
  Purchase #5 $173.88   7.553%   $187.0132   $187.01   $187.00   $187.00  
  Purchase #6 $86.28   8.141%   $93.3041   $93.30   $93.30   $93.30  
  Purchase #7 $131.45   11.228%   $146.2092   $146.21   $146.20   $146.20  
  7 purchase totals = $896.05       $975.5565   $975.55   $975.55   $975.50