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 $152.52   7.707%   $164.2747   $164.27   $164.25   $164.30  
  Purchase #2 $56.37   5.555%   $59.5014   $59.50   $59.50   $59.50  
  Purchase #3 $131.55   13.563%   $149.3921   $149.39   $149.40   $149.40  
  Purchase #4 $249.39   5.349%   $262.7299   $262.73   $262.75   $262.70  
  Purchase #5 $71.70   10.856%   $79.4838   $79.48   $79.50   $79.50  
  Purchase #6 $211.40   12.753%   $238.3598   $238.36   $238.35   $238.40  
  Purchase #7 $86.68   9.618%   $95.0169   $95.02   $95.00   $95.00  
  7 purchase totals = $959.61       $1,048.7586   $1,048.75   $1,048.75   $1,048.80