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 $52.61   7.774%   $56.6999   $56.70   $56.70   $56.70  
  Purchase #2 $78.97   4.136%   $82.2362   $82.24   $82.25   $82.20  
  Purchase #3 $193.27   4.153%   $201.2965   $201.30   $201.30   $201.30  
  Purchase #4 $238.98   13.693%   $271.7035   $271.70   $271.70   $271.70  
  Purchase #5 $119.94   9.805%   $131.7001   $131.70   $131.70   $131.70  
  Purchase #6 $15.91   12.746%   $17.9379   $17.94   $17.95   $17.90  
  Purchase #7 $160.45   12.716%   $180.8528   $180.85   $180.85   $180.90  
  7 purchase totals = $860.13       $942.4269   $942.43   $942.45   $942.40