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 $33.66   3.122%   $34.7109   $34.71   $34.70   $34.70  
  Purchase #2 $229.32   5.387%   $241.6735   $241.67   $241.65   $241.70  
  Purchase #3 $162.59   12.114%   $182.2862   $182.29   $182.30   $182.30  
  Purchase #4 $170.90   10.291%   $188.4873   $188.49   $188.50   $188.50  
  Purchase #5 $78.44   11.790%   $87.6881   $87.69   $87.70   $87.70  
  Purchase #6 $206.26   10.674%   $228.2762   $228.28   $228.30   $228.30  
  Purchase #7 $106.77   11.654%   $119.213   $119.21   $119.20   $119.20  
  7 purchase totals = $987.94       $1,082.3352   $1,082.34   $1,082.35   $1,082.40