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 $60.88   6.761%   $64.9961   $65.00   $65.00   $65.00  
  Purchase #2 $151.57   7.523%   $162.9726   $162.97   $162.95   $163.00  
  Purchase #3 $145.64   12.197%   $163.4037   $163.40   $163.40   $163.40  
  Purchase #4 $36.81   11.799%   $41.1532   $41.15   $41.15   $41.20  
  Purchase #5 $128.98   7.564%   $138.736   $138.74   $138.75   $138.70  
  Purchase #6 $161.33   4.795%   $169.0658   $169.07   $169.05   $169.10  
  Purchase #7 $153.98   10.736%   $170.5113   $170.51   $170.50   $170.50  
  7 purchase totals = $839.19       $910.8387   $910.84   $910.80   $910.90