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 $211.25   4.816%   $221.4238   $221.42   $221.40   $221.40  
  Purchase #2 $209.71   5.863%   $222.0053   $222.01   $222.00   $222.00  
  Purchase #3 $29.44   6.121%   $31.242   $31.24   $31.25   $31.20  
  Purchase #4 $179.35   5.551%   $189.3057   $189.31   $189.30   $189.30  
  Purchase #5 $177.32   9.339%   $193.8799   $193.88   $193.90   $193.90  
  Purchase #6 $164.61   11.306%   $183.2208   $183.22   $183.20   $183.20  
  Purchase #7 $203.78   11.316%   $226.8397   $226.84   $226.85   $226.80  
  7 purchase totals = $1,175.46       $1,267.9172   $1,267.92   $1,267.90   $1,267.80