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 $67.39   8.576%   $73.1694   $73.17   $73.15   $73.20  
  Purchase #2 $199.30   7.620%   $214.4867   $214.49   $214.50   $214.50  
  Purchase #3 $205.87   11.236%   $229.0016   $229.00   $229.00   $229.00  
  Purchase #4 $92.51   9.479%   $101.279   $101.28   $101.30   $101.30  
  Purchase #5 $246.72   13.320%   $279.5831   $279.58   $279.60   $279.60  
  Purchase #6 $210.96   8.613%   $229.13   $229.13   $229.15   $229.10  
  Purchase #7 $34.49   7.293%   $37.0054   $37.01   $37.00   $37.00  
  7 purchase totals = $1,057.24       $1,163.6552   $1,163.66   $1,163.70   $1,163.70