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 $180.77   7.332%   $194.0241   $194.02   $194.00   $194.00  
  Purchase #2 $105.79   4.774%   $110.8404   $110.84   $110.85   $110.80  
  Purchase #3 $109.42   9.295%   $119.5906   $119.59   $119.60   $119.60  
  Purchase #4 $201.56   4.133%   $209.8905   $209.89   $209.90   $209.90  
  Purchase #5 $126.33   7.612%   $135.9462   $135.95   $135.95   $135.90  
  Purchase #6 $243.41   7.558%   $261.8069   $261.81   $261.80   $261.80  
  Purchase #7 $250.89   11.166%   $278.9044   $278.90   $278.90   $278.90  
  7 purchase totals = $1,218.17       $1,311.0031   $1,311.00   $1,311.00   $1,310.90