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 $118.72   11.739%   $132.6565   $132.66   $132.65   $132.70  
  Purchase #2 $199.55   11.607%   $222.7118   $222.71   $222.70   $222.70  
  Purchase #3 $239.72   3.807%   $248.8461   $248.85   $248.85   $248.80  
  Purchase #4 $173.82   7.109%   $186.1769   $186.18   $186.20   $186.20  
  Purchase #5 $8.59   7.698%   $9.2513   $9.25   $9.25   $9.30  
  Purchase #6 $126.49   9.273%   $138.2194   $138.22   $138.20   $138.20  
  Purchase #7 $110.55   7.398%   $118.7285   $118.73   $118.75   $118.70  
  7 purchase totals = $977.44       $1,056.5905   $1,056.60   $1,056.60   $1,056.60