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 $228.92   6.154%   $243.0077   $243.01   $243.00   $243.00  
  Purchase #2 $172.30   6.334%   $183.2135   $183.21   $183.20   $183.20  
  Purchase #3 $202.86   4.224%   $211.4288   $211.43   $211.45   $211.40  
  Purchase #4 $58.66   10.227%   $64.6592   $64.66   $64.65   $64.70  
  Purchase #5 $103.89   5.786%   $109.9011   $109.90   $109.90   $109.90  
  Purchase #6 $233.32   11.851%   $260.9708   $260.97   $260.95   $261.00  
  Purchase #7 $165.49   13.421%   $187.7004   $187.70   $187.70   $187.70  
  7 purchase totals = $1,165.44       $1,260.8815   $1,260.88   $1,260.85   $1,260.90