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 $238.82   12.713%   $269.1812   $269.18   $269.20   $269.20  
  Purchase #2 $24.51   3.521%   $25.373   $25.37   $25.35   $25.40  
  Purchase #3 $83.94   3.692%   $87.0391   $87.04   $87.05   $87.00  
  Purchase #4 $129.38   9.568%   $141.7591   $141.76   $141.75   $141.80  
  Purchase #5 $104.91   12.588%   $118.1161   $118.12   $118.10   $118.10  
  Purchase #6 $50.63   11.164%   $56.2823   $56.28   $56.30   $56.30  
  Purchase #7 $61.82   12.399%   $69.4851   $69.49   $69.50   $69.50  
  7 purchase totals = $694.01       $767.2359   $767.24   $767.25   $767.30