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 $59.43   13.606%   $67.516   $67.52   $67.50   $67.50  
  Purchase #2 $88.72   10.228%   $97.7943   $97.79   $97.80   $97.80  
  Purchase #3 $196.94   6.755%   $210.2433   $210.24   $210.25   $210.20  
  Purchase #4 $16.31   6.260%   $17.331   $17.33   $17.35   $17.30  
  Purchase #5 $182.78   13.485%   $207.4279   $207.43   $207.45   $207.40  
  Purchase #6 $151.86   5.304%   $159.9147   $159.91   $159.90   $159.90  
  Purchase #7 $145.58   6.544%   $155.1068   $155.11   $155.10   $155.10  
  7 purchase totals = $841.62       $915.3340   $915.33   $915.35   $915.20