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 $76.69   12.541%   $86.3077   $86.31   $86.30   $86.30  
  Purchase #2 $73.34   4.132%   $76.3704   $76.37   $76.35   $76.40  
  Purchase #3 $204.61   3.763%   $212.3095   $212.31   $212.30   $212.30  
  Purchase #4 $234.94   4.874%   $246.391   $246.39   $246.40   $246.40  
  Purchase #5 $101.92   8.193%   $110.2703   $110.27   $110.25   $110.30  
  Purchase #6 $135.69   5.532%   $143.1964   $143.20   $143.20   $143.20  
  Purchase #7 $196.54   13.863%   $223.7863   $223.79   $223.80   $223.80  
  7 purchase totals = $1,023.73       $1,098.6316   $1,098.64   $1,098.60   $1,098.70