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 $67.43   13.162%   $76.3051   $76.31   $76.30   $76.30  
  Purchase #2 $193.96   9.349%   $212.0933   $212.09   $212.10   $212.10  
  Purchase #3 $93.28   4.249%   $97.2435   $97.24   $97.25   $97.20  
  Purchase #4 $149.32   11.227%   $166.0842   $166.08   $166.10   $166.10  
  Purchase #5 $122.48   8.780%   $133.2337   $133.23   $133.25   $133.20  
  Purchase #6 $159.50   13.162%   $180.4934   $180.49   $180.50   $180.50  
  Purchase #7 $200.94   6.297%   $213.5932   $213.59   $213.60   $213.60  
  7 purchase totals = $986.91       $1,079.0464   $1,079.03   $1,079.10   $1,079.00