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 $182.26   12.562%   $205.1555   $205.16   $205.15   $205.20  
  Purchase #2 $98.79   9.521%   $108.1958   $108.20   $108.20   $108.20  
  Purchase #3 $194.28   11.467%   $216.5581   $216.56   $216.55   $216.60  
  Purchase #4 $208.96   13.132%   $236.4006   $236.40   $236.40   $236.40  
  Purchase #5 $36.85   9.276%   $40.2682   $40.27   $40.25   $40.30  
  Purchase #6 $151.46   9.222%   $165.4276   $165.43   $165.45   $165.40  
  Purchase #7 $38.55   3.728%   $39.9871   $39.99   $40.00   $40.00  
  7 purchase totals = $911.15       $1,011.9929   $1,012.01   $1,012.00   $1,012.10