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 $52.34   13.203%   $59.2505   $59.25   $59.25   $59.30  
  Purchase #2 $233.66   6.580%   $249.0348   $249.03   $249.05   $249.00  
  Purchase #3 $177.73   6.865%   $189.9312   $189.93   $189.95   $189.90  
  Purchase #4 $115.57   10.378%   $127.5639   $127.56   $127.55   $127.60  
  Purchase #5 $95.86   11.286%   $106.6788   $106.68   $106.70   $106.70  
  Purchase #6 $135.28   7.825%   $145.8657   $145.87   $145.85   $145.90  
  Purchase #7 $234.79   4.242%   $244.7498   $244.75   $244.75   $244.70  
  7 purchase totals = $1,045.23       $1,123.0747   $1,123.07   $1,123.10   $1,123.10