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 $191.29   6.707%   $204.1198   $204.12   $204.10   $204.10  
  Purchase #2 $56.43   12.241%   $63.3376   $63.34   $63.35   $63.30  
  Purchase #3 $127.26   5.763%   $134.594   $134.59   $134.60   $134.60  
  Purchase #4 $179.57   12.871%   $202.6825   $202.68   $202.70   $202.70  
  Purchase #5 $15.98   12.224%   $17.9334   $17.93   $17.95   $17.90  
  Purchase #6 $58.31   5.614%   $61.5835   $61.58   $61.60   $61.60  
  Purchase #7 $234.55   9.784%   $257.4984   $257.50   $257.50   $257.50  
  7 purchase totals = $863.39       $941.7492   $941.74   $941.80   $941.70