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 $83.33   13.495%   $94.5754   $94.58   $94.60   $94.60  
  Purchase #2 $243.35   6.873%   $260.0754   $260.08   $260.10   $260.10  
  Purchase #3 $207.82   4.621%   $217.4234   $217.42   $217.40   $217.40  
  Purchase #4 $101.72   4.716%   $106.5171   $106.52   $106.50   $106.50  
  Purchase #5 $175.80   13.423%   $199.3976   $199.40   $199.40   $199.40  
  Purchase #6 $10.52   11.454%   $11.725   $11.73   $11.75   $11.70  
  Purchase #7 $227.30   5.578%   $239.9788   $239.98   $240.00   $240.00  
  7 purchase totals = $1,049.84       $1,129.6927   $1,129.71   $1,129.75   $1,129.70