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 $85.66   6.260%   $91.0223   $91.02   $91.00   $91.00  
  Purchase #2 $199.63   5.209%   $210.0287   $210.03   $210.05   $210.00  
  Purchase #3 $113.85   6.519%   $121.2719   $121.27   $121.25   $121.30  
  Purchase #4 $171.75   7.439%   $184.5265   $184.53   $184.55   $184.50  
  Purchase #5 $226.49   7.728%   $243.9931   $243.99   $244.00   $244.00  
  Purchase #6 $24.76   5.653%   $26.1597   $26.16   $26.15   $26.20  
  Purchase #7 $65.71   12.263%   $73.768   $73.77   $73.75   $73.80  
  7 purchase totals = $887.85       $950.7702   $950.77   $950.75   $950.80