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 $226.97   11.678%   $253.4756   $253.48   $253.50   $253.50  
  Purchase #2 $50.37   11.578%   $56.2018   $56.20   $56.20   $56.20  
  Purchase #3 $170.73   6.744%   $182.244   $182.24   $182.25   $182.20  
  Purchase #4 $81.42   7.199%   $87.2814   $87.28   $87.30   $87.30  
  Purchase #5 $237.72   13.212%   $269.1276   $269.13   $269.15   $269.10  
  Purchase #6 $190.64   10.858%   $211.3397   $211.34   $211.35   $211.30  
  Purchase #7 $145.93   8.695%   $158.6186   $158.62   $158.60   $158.60  
  7 purchase totals = $1,103.78       $1,218.2887   $1,218.29   $1,218.35   $1,218.20