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 $182.67   4.697%   $191.25   $191.25   $191.25   $191.30  
  Purchase #2 $122.45   11.613%   $136.6701   $136.67   $136.65   $136.70  
  Purchase #3 $30.81   12.641%   $34.7047   $34.70   $34.70   $34.70  
  Purchase #4 $180.33   8.450%   $195.5679   $195.57   $195.55   $195.60  
  Purchase #5 $138.48   5.180%   $145.6533   $145.65   $145.65   $145.70  
  Purchase #6 $111.89   7.113%   $119.8487   $119.85   $119.85   $119.80  
  Purchase #7 $107.39   10.674%   $118.8528   $118.85   $118.85   $118.90  
  7 purchase totals = $874.02       $942.5475   $942.54   $942.50   $942.70