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 $229.93   10.456%   $253.9715   $253.97   $253.95   $254.00  
  Purchase #2 $138.49   8.536%   $150.3115   $150.31   $150.30   $150.30  
  Purchase #3 $183.41   13.188%   $207.5981   $207.60   $207.60   $207.60  
  Purchase #4 $228.29   7.184%   $244.6904   $244.69   $244.70   $244.70  
  Purchase #5 $9.91   4.642%   $10.37   $10.37   $10.35   $10.40  
  Purchase #6 $230.56   11.789%   $257.7407   $257.74   $257.75   $257.70  
  Purchase #7 $158.50   11.558%   $176.8194   $176.82   $176.80   $176.80  
  7 purchase totals = $1,179.09       $1,301.5016   $1,301.50   $1,301.45   $1,301.50