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 $55.90   13.168%   $63.2609   $63.26   $63.25   $63.30  
  Purchase #2 $184.98   13.529%   $210.0059   $210.01   $210.00   $210.00  
  Purchase #3 $71.28   9.375%   $77.9625   $77.96   $77.95   $78.00  
  Purchase #4 $216.55   11.284%   $240.9855   $240.99   $241.00   $241.00  
  Purchase #5 $104.87   11.306%   $116.7266   $116.73   $116.75   $116.70  
  Purchase #6 $168.81   7.162%   $180.9002   $180.90   $180.90   $180.90  
  Purchase #7 $216.75   7.199%   $232.3538   $232.35   $232.35   $232.40  
  7 purchase totals = $1,019.14       $1,122.1954   $1,122.20   $1,122.20   $1,122.30