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 $196.35   9.319%   $214.6479   $214.65   $214.65   $214.60  
  Purchase #2 $76.80   11.282%   $85.4646   $85.46   $85.45   $85.50  
  Purchase #3 $53.84   5.543%   $56.8244   $56.82   $56.80   $56.80  
  Purchase #4 $231.44   7.502%   $248.8026   $248.80   $248.80   $248.80  
  Purchase #5 $72.84   5.193%   $76.6226   $76.62   $76.60   $76.60  
  Purchase #6 $221.68   10.219%   $244.3335   $244.33   $244.35   $244.30  
  Purchase #7 $73.33   10.429%   $80.9776   $80.98   $81.00   $81.00  
  7 purchase totals = $926.28       $1,007.6732   $1,007.66   $1,007.65   $1,007.60