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 $35.72   3.416%   $36.9402   $36.94   $36.95   $36.90  
  Purchase #2 $192.61   7.593%   $207.2349   $207.23   $207.25   $207.20  
  Purchase #3 $80.59   9.422%   $88.1832   $88.18   $88.20   $88.20  
  Purchase #4 $46.61   12.198%   $52.2955   $52.30   $52.30   $52.30  
  Purchase #5 $247.61   7.478%   $266.1263   $266.13   $266.15   $266.10  
  Purchase #6 $246.48   5.799%   $260.7734   $260.77   $260.75   $260.80  
  Purchase #7 $83.77   8.660%   $91.0245   $91.02   $91.00   $91.00  
  7 purchase totals = $933.39       $1,002.5780   $1,002.57   $1,002.60   $1,002.50