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 $54.92   10.348%   $60.6031   $60.60   $60.60   $60.60  
  Purchase #2 $120.55   10.439%   $133.1342   $133.13   $133.15   $133.10  
  Purchase #3 $10.59   13.671%   $12.0378   $12.04   $12.05   $12.00  
  Purchase #4 $177.84   5.216%   $187.1161   $187.12   $187.10   $187.10  
  Purchase #5 $159.33   6.425%   $169.567   $169.57   $169.55   $169.60  
  Purchase #6 $120.61   11.249%   $134.1774   $134.18   $134.20   $134.20  
  Purchase #7 $231.48   9.660%   $253.841   $253.84   $253.85   $253.80  
  7 purchase totals = $875.32       $950.4766   $950.48   $950.50   $950.40