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 $235.95   11.796%   $263.7827   $263.78   $263.80   $263.80  
  Purchase #2 $196.79   4.319%   $205.2894   $205.29   $205.30   $205.30  
  Purchase #3 $24.66   4.145%   $25.6822   $25.68   $25.70   $25.70  
  Purchase #4 $67.49   3.454%   $69.8211   $69.82   $69.80   $69.80  
  Purchase #5 $131.74   3.109%   $135.8358   $135.84   $135.85   $135.80  
  Purchase #6 $36.26   8.802%   $39.4516   $39.45   $39.45   $39.50  
  Purchase #7 $239.89   11.233%   $266.8368   $266.84   $266.85   $266.80  
  7 purchase totals = $932.78       $1,006.6996   $1,006.70   $1,006.75   $1,006.70