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 $65.75   11.868%   $73.5532   $73.55   $73.55   $73.60  
  Purchase #2 $198.27   3.336%   $204.8843   $204.88   $204.90   $204.90  
  Purchase #3 $106.28   6.341%   $113.0192   $113.02   $113.00   $113.00  
  Purchase #4 $106.59   5.497%   $112.4493   $112.45   $112.45   $112.40  
  Purchase #5 $111.35   13.277%   $126.1339   $126.13   $126.15   $126.10  
  Purchase #6 $141.40   3.115%   $145.8046   $145.80   $145.80   $145.80  
  Purchase #7 $234.48   9.441%   $256.6173   $256.62   $256.60   $256.60  
  7 purchase totals = $964.12       $1,032.4618   $1,032.45   $1,032.45   $1,032.40