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 $234.95   5.258%   $247.3037   $247.30   $247.30   $247.30  
  Purchase #2 $226.39   3.369%   $234.0171   $234.02   $234.00   $234.00  
  Purchase #3 $28.26   8.269%   $30.5968   $30.60   $30.60   $30.60  
  Purchase #4 $45.51   6.521%   $48.4777   $48.48   $48.50   $48.50  
  Purchase #5 $246.39   7.402%   $264.6278   $264.63   $264.65   $264.60  
  Purchase #6 $101.39   5.420%   $106.8853   $106.89   $106.90   $106.90  
  Purchase #7 $111.37   9.726%   $122.2018   $122.20   $122.20   $122.20  
  7 purchase totals = $994.26       $1,054.1102   $1,054.12   $1,054.15   $1,054.10