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 $96.68   10.433%   $106.7666   $106.77   $106.75   $106.80  
  Purchase #2 $57.54   11.579%   $64.2026   $64.20   $64.20   $64.20  
  Purchase #3 $29.45   13.678%   $33.4782   $33.48   $33.50   $33.50  
  Purchase #4 $163.81   13.141%   $185.3363   $185.34   $185.35   $185.30  
  Purchase #5 $23.73   12.280%   $26.644   $26.64   $26.65   $26.60  
  Purchase #6 $38.95   10.200%   $42.9229   $42.92   $42.90   $42.90  
  Purchase #7 $211.37   6.216%   $224.5088   $224.51   $224.50   $224.50  
  7 purchase totals = $621.53       $683.8594   $683.86   $683.85   $683.80