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 $191.96   6.732%   $204.8827   $204.88   $204.90   $204.90  
  Purchase #2 $243.87   6.665%   $260.1239   $260.12   $260.10   $260.10  
  Purchase #3 $63.60   8.465%   $68.9837   $68.98   $69.00   $69.00  
  Purchase #4 $193.72   12.520%   $217.9737   $217.97   $217.95   $218.00  
  Purchase #5 $204.85   11.356%   $228.1128   $228.11   $228.10   $228.10  
  Purchase #6 $193.31   8.128%   $209.0222   $209.02   $209.00   $209.00  
  Purchase #7 $10.49   7.178%   $11.243   $11.24   $11.25   $11.20  
  7 purchase totals = $1,101.80       $1,200.3420   $1,200.32   $1,200.30   $1,200.30