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 $116.74   8.846%   $127.0668   $127.07   $127.05   $127.10  
  Purchase #2 $151.53   12.236%   $170.0712   $170.07   $170.05   $170.10  
  Purchase #3 $47.66   7.194%   $51.0887   $51.09   $51.10   $51.10  
  Purchase #4 $47.52   10.233%   $52.3827   $52.38   $52.40   $52.40  
  Purchase #5 $239.77   6.294%   $254.8611   $254.86   $254.85   $254.90  
  Purchase #6 $65.64   13.179%   $74.2907   $74.29   $74.30   $74.30  
  Purchase #7 $159.70   7.764%   $172.0991   $172.10   $172.10   $172.10  
  7 purchase totals = $828.56       $901.8603   $901.86   $901.85   $902.00