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 $69.39   9.202%   $75.7753   $75.78   $75.80   $75.80  
  Purchase #2 $160.41   4.610%   $167.8049   $167.80   $167.80   $167.80  
  Purchase #3 $64.94   7.350%   $69.7131   $69.71   $69.70   $69.70  
  Purchase #4 $230.66   9.521%   $252.6211   $252.62   $252.60   $252.60  
  Purchase #5 $91.37   4.295%   $95.2943   $95.29   $95.30   $95.30  
  Purchase #6 $131.38   8.109%   $142.0336   $142.03   $142.05   $142.00  
  Purchase #7 $135.48   5.575%   $143.033   $143.03   $143.05   $143.00  
  7 purchase totals = $883.63       $946.2753   $946.26   $946.30   $946.20