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 $160.94   8.530%   $174.6682   $174.67   $174.65   $174.70  
  Purchase #2 $119.40   11.817%   $133.5095   $133.51   $133.50   $133.50  
  Purchase #3 $53.37   11.609%   $59.5657   $59.57   $59.55   $59.60  
  Purchase #4 $21.89   12.696%   $24.6692   $24.67   $24.65   $24.70  
  Purchase #5 $49.84   3.348%   $51.5086   $51.51   $51.50   $51.50  
  Purchase #6 $187.72   11.700%   $209.6832   $209.68   $209.70   $209.70  
  Purchase #7 $57.30   12.819%   $64.6453   $64.65   $64.65   $64.60  
  7 purchase totals = $650.46       $718.2497   $718.26   $718.20   $718.30