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 $134.78   6.652%   $143.7456   $143.75   $143.75   $143.70  
  Purchase #2 $187.39   10.597%   $207.2477   $207.25   $207.25   $207.20  
  Purchase #3 $134.93   10.409%   $148.9749   $148.97   $148.95   $149.00  
  Purchase #4 $166.30   7.604%   $178.9455   $178.95   $178.95   $178.90  
  Purchase #5 $93.59   13.298%   $106.0356   $106.04   $106.05   $106.00  
  Purchase #6 $13.84   5.780%   $14.64   $14.64   $14.65   $14.60  
  Purchase #7 $239.44   6.811%   $255.7483   $255.75   $255.75   $255.70  
  7 purchase totals = $970.27       $1,055.3376   $1,055.35   $1,055.35   $1,055.10