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 $217.97   12.220%   $244.6059   $244.61   $244.60   $244.60  
  Purchase #2 $169.37   7.499%   $182.0711   $182.07   $182.05   $182.10  
  Purchase #3 $139.57   11.854%   $156.1146   $156.11   $156.10   $156.10  
  Purchase #4 $94.39   7.102%   $101.0936   $101.09   $101.10   $101.10  
  Purchase #5 $201.98   8.241%   $218.6252   $218.63   $218.65   $218.60  
  Purchase #6 $150.70   4.106%   $156.8877   $156.89   $156.90   $156.90  
  Purchase #7 $193.33   8.113%   $209.0149   $209.01   $209.00   $209.00  
  7 purchase totals = $1,167.31       $1,268.4130   $1,268.41   $1,268.40   $1,268.40