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 $88.88   5.667%   $93.9168   $93.92   $93.90   $93.90  
  Purchase #2 $81.65   4.348%   $85.2001   $85.20   $85.20   $85.20  
  Purchase #3 $173.51   8.341%   $187.9825   $187.98   $188.00   $188.00  
  Purchase #4 $159.79   8.510%   $173.3881   $173.39   $173.40   $173.40  
  Purchase #5 $67.54   7.693%   $72.7359   $72.74   $72.75   $72.70  
  Purchase #6 $177.99   7.366%   $191.1007   $191.10   $191.10   $191.10  
  Purchase #7 $188.59   12.431%   $212.0336   $212.03   $212.05   $212.00  
  7 purchase totals = $937.95       $1,016.3577   $1,016.36   $1,016.40   $1,016.30