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 $42.26   12.668%   $47.6135   $47.61   $47.60   $47.60  
  Purchase #2 $154.51   12.732%   $174.1822   $174.18   $174.20   $174.20  
  Purchase #3 $112.98   6.857%   $120.727   $120.73   $120.75   $120.70  
  Purchase #4 $223.95   3.580%   $231.9674   $231.97   $231.95   $232.00  
  Purchase #5 $151.62   9.585%   $166.1528   $166.15   $166.15   $166.20  
  Purchase #6 $171.71   9.255%   $187.6018   $187.60   $187.60   $187.60  
  Purchase #7 $29.26   10.825%   $32.4274   $32.43   $32.45   $32.40  
  7 purchase totals = $886.29       $960.6721   $960.67   $960.70   $960.70