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 $174.61   11.567%   $194.8071   $194.81   $194.80   $194.80  
  Purchase #2 $65.61   11.819%   $73.3644   $73.36   $73.35   $73.40  
  Purchase #3 $106.75   10.336%   $117.7837   $117.78   $117.80   $117.80  
  Purchase #4 $85.78   5.867%   $90.8127   $90.81   $90.80   $90.80  
  Purchase #5 $179.84   13.749%   $204.5662   $204.57   $204.55   $204.60  
  Purchase #6 $132.27   5.283%   $139.2578   $139.26   $139.25   $139.30  
  Purchase #7 $149.35   12.334%   $167.7708   $167.77   $167.75   $167.80  
  7 purchase totals = $894.21       $988.3627   $988.36   $988.30   $988.50