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 $33.74   9.388%   $36.9075   $36.91   $36.90   $36.90  
  Purchase #2 $219.87   6.507%   $234.1769   $234.18   $234.20   $234.20  
  Purchase #3 $7.44   11.607%   $8.3036   $8.30   $8.30   $8.30  
  Purchase #4 $194.30   6.482%   $206.8945   $206.89   $206.90   $206.90  
  Purchase #5 $147.39   4.701%   $154.3188   $154.32   $154.30   $154.30  
  Purchase #6 $244.90   9.228%   $267.4994   $267.50   $267.50   $267.50  
  Purchase #7 $95.50   5.438%   $100.6933   $100.69   $100.70   $100.70  
  7 purchase totals = $943.14       $1,008.7940   $1,008.79   $1,008.80   $1,008.80