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 $87.99   4.222%   $91.7049   $91.70   $91.70   $91.70  
  Purchase #2 $64.88   8.329%   $70.2839   $70.28   $70.30   $70.30  
  Purchase #3 $51.43   12.554%   $57.8865   $57.89   $57.90   $57.90  
  Purchase #4 $241.44   5.647%   $255.0741   $255.07   $255.05   $255.10  
  Purchase #5 $227.27   9.428%   $248.697   $248.70   $248.70   $248.70  
  Purchase #6 $148.58   3.106%   $153.1949   $153.19   $153.20   $153.20  
  Purchase #7 $156.50   9.514%   $171.3894   $171.39   $171.40   $171.40  
  7 purchase totals = $978.09       $1,048.2307   $1,048.22   $1,048.25   $1,048.30