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 $241.27   8.798%   $262.4969   $262.50   $262.50   $262.50  
  Purchase #2 $189.45   6.797%   $202.3269   $202.33   $202.35   $202.30  
  Purchase #3 $104.91   11.372%   $116.8404   $116.84   $116.85   $116.80  
  Purchase #4 $8.94   13.507%   $10.1475   $10.15   $10.15   $10.10  
  Purchase #5 $194.37   5.869%   $205.7776   $205.78   $205.80   $205.80  
  Purchase #6 $131.44   4.855%   $137.8214   $137.82   $137.80   $137.80  
  Purchase #7 $71.64   3.134%   $73.8852   $73.89   $73.90   $73.90  
  7 purchase totals = $942.02       $1,009.2959   $1,009.31   $1,009.35   $1,009.20