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 $22.90   13.467%   $25.9839   $25.98   $26.00   $26.00  
  Purchase #2 $36.40   8.163%   $39.3713   $39.37   $39.35   $39.40  
  Purchase #3 $145.39   7.543%   $156.3568   $156.36   $156.35   $156.40  
  Purchase #4 $241.59   7.761%   $260.3398   $260.34   $260.35   $260.30  
  Purchase #5 $176.89   10.571%   $195.589   $195.59   $195.60   $195.60  
  Purchase #6 $164.53   9.619%   $180.3561   $180.36   $180.35   $180.40  
  Purchase #7 $141.93   9.592%   $155.5439   $155.54   $155.55   $155.50  
  7 purchase totals = $929.63       $1,013.5408   $1,013.54   $1,013.55   $1,013.60