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 $11.34   6.203%   $12.0434   $12.04   $12.05   $12.00  
  Purchase #2 $101.63   4.587%   $106.2918   $106.29   $106.30   $106.30  
  Purchase #3 $212.92   10.840%   $236.0005   $236.00   $236.00   $236.00  
  Purchase #4 $202.53   6.735%   $216.1704   $216.17   $216.15   $216.20  
  Purchase #5 $24.88   8.566%   $27.0112   $27.01   $27.00   $27.00  
  Purchase #6 $220.33   6.852%   $235.427   $235.43   $235.45   $235.40  
  Purchase #7 $162.85   6.692%   $173.7479   $173.75   $173.75   $173.70  
  7 purchase totals = $936.48       $1,006.6922   $1,006.69   $1,006.70   $1,006.60