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 $169.97   6.580%   $181.154   $181.15   $181.15   $181.20  
  Purchase #2 $146.41   6.654%   $156.1521   $156.15   $156.15   $156.20  
  Purchase #3 $52.84   13.477%   $59.9612   $59.96   $59.95   $60.00  
  Purchase #4 $153.39   10.251%   $169.114   $169.11   $169.10   $169.10  
  Purchase #5 $6.60   8.286%   $7.1469   $7.15   $7.15   $7.10  
  Purchase #6 $13.60   4.664%   $14.2343   $14.23   $14.25   $14.20  
  Purchase #7 $163.38   10.512%   $180.5545   $180.55   $180.55   $180.60  
  7 purchase totals = $706.19       $768.3170   $768.30   $768.30   $768.40