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 $13.28   11.463%   $14.8023   $14.80   $14.80   $14.80  
  Purchase #2 $184.30   6.160%   $195.6529   $195.65   $195.65   $195.70  
  Purchase #3 $18.28   12.211%   $20.5122   $20.51   $20.50   $20.50  
  Purchase #4 $179.64   4.534%   $187.7849   $187.78   $187.80   $187.80  
  Purchase #5 $226.88   11.386%   $252.7126   $252.71   $252.70   $252.70  
  Purchase #6 $176.92   13.231%   $200.3283   $200.33   $200.35   $200.30  
  Purchase #7 $224.42   5.125%   $235.9215   $235.92   $235.90   $235.90  
  7 purchase totals = $1,023.72       $1,107.7147   $1,107.70   $1,107.70   $1,107.70