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 $242.58   3.566%   $251.2304   $251.23   $251.25   $251.20  
  Purchase #2 $51.69   5.322%   $54.4409   $54.44   $54.45   $54.40  
  Purchase #3 $132.55   8.306%   $143.5596   $143.56   $143.55   $143.60  
  Purchase #4 $189.60   6.278%   $201.5031   $201.50   $201.50   $201.50  
  Purchase #5 $9.61   6.620%   $10.2462   $10.25   $10.25   $10.20  
  Purchase #6 $183.68   11.746%   $205.2551   $205.26   $205.25   $205.30  
  Purchase #7 $147.70   12.848%   $166.6765   $166.68   $166.70   $166.70  
  7 purchase totals = $957.41       $1,032.9118   $1,032.92   $1,032.95   $1,032.90