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 $249.33   8.600%   $270.7724   $270.77   $270.75   $270.80  
  Purchase #2 $119.84   8.150%   $129.607   $129.61   $129.60   $129.60  
  Purchase #3 $19.89   8.613%   $21.6031   $21.60   $21.60   $21.60  
  Purchase #4 $152.60   12.446%   $171.5926   $171.59   $171.60   $171.60  
  Purchase #5 $147.88   12.519%   $166.3931   $166.39   $166.40   $166.40  
  Purchase #6 $245.97   10.299%   $271.3025   $271.30   $271.30   $271.30  
  Purchase #7 $90.75   11.245%   $100.9548   $100.95   $100.95   $101.00  
  7 purchase totals = $1,026.26       $1,132.2255   $1,132.21   $1,132.20   $1,132.30