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 $63.41   11.347%   $70.6051   $70.61   $70.60   $70.60  
  Purchase #2 $103.56   12.341%   $116.3403   $116.34   $116.35   $116.30  
  Purchase #3 $197.96   13.820%   $225.3181   $225.32   $225.30   $225.30  
  Purchase #4 $201.26   9.686%   $220.754   $220.75   $220.75   $220.80  
  Purchase #5 $5.60   9.609%   $6.1381   $6.14   $6.15   $6.10  
  Purchase #6 $141.57   6.534%   $150.8202   $150.82   $150.80   $150.80  
  Purchase #7 $59.39   10.848%   $65.8326   $65.83   $65.85   $65.80  
  7 purchase totals = $772.75       $855.8084   $855.81   $855.80   $855.70