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 $192.74   4.816%   $202.0224   $202.02   $202.00   $202.00  
  Purchase #2 $214.71   8.526%   $233.0162   $233.02   $233.00   $233.00  
  Purchase #3 $133.40   12.673%   $150.3058   $150.31   $150.30   $150.30  
  Purchase #4 $232.39   5.696%   $245.6269   $245.63   $245.65   $245.60  
  Purchase #5 $132.79   6.313%   $141.173   $141.17   $141.15   $141.20  
  Purchase #6 $26.47   7.442%   $28.4399   $28.44   $28.45   $28.40  
  Purchase #7 $187.89   12.253%   $210.9122   $210.91   $210.90   $210.90  
  7 purchase totals = $1,120.39       $1,211.4964   $1,211.50   $1,211.45   $1,211.40