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 $232.34   4.564%   $242.944   $242.94   $242.95   $242.90  
  Purchase #2 $54.55   10.306%   $60.1719   $60.17   $60.15   $60.20  
  Purchase #3 $165.96   10.525%   $183.4273   $183.43   $183.45   $183.40  
  Purchase #4 $59.56   10.297%   $65.6929   $65.69   $65.70   $65.70  
  Purchase #5 $246.98   9.559%   $270.5888   $270.59   $270.60   $270.60  
  Purchase #6 $212.40   10.294%   $234.2645   $234.26   $234.25   $234.30  
  Purchase #7 $232.63   5.472%   $245.3595   $245.36   $245.35   $245.40  
  7 purchase totals = $1,204.42       $1,302.4489   $1,302.44   $1,302.45   $1,302.50