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 $209.61   13.260%   $237.4043   $237.40   $237.40   $237.40  
  Purchase #2 $179.92   13.678%   $204.5295   $204.53   $204.55   $204.50  
  Purchase #3 $133.98   8.319%   $145.1258   $145.13   $145.15   $145.10  
  Purchase #4 $58.68   3.674%   $60.8359   $60.84   $60.85   $60.80  
  Purchase #5 $236.39   4.362%   $246.7013   $246.70   $246.70   $246.70  
  Purchase #6 $5.83   8.567%   $6.3295   $6.33   $6.35   $6.30  
  Purchase #7 $246.25   3.425%   $254.6841   $254.68   $254.70   $254.70  
  7 purchase totals = $1,070.66       $1,155.6104   $1,155.61   $1,155.70   $1,155.50