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 $92.34   7.449%   $99.2184   $99.22   $99.20   $99.20  
  Purchase #2 $248.36   9.494%   $271.9393   $271.94   $271.95   $271.90  
  Purchase #3 $170.68   8.828%   $185.7476   $185.75   $185.75   $185.70  
  Purchase #4 $40.65   9.205%   $44.3918   $44.39   $44.40   $44.40  
  Purchase #5 $72.26   7.772%   $77.876   $77.88   $77.90   $77.90  
  Purchase #6 $213.34   5.632%   $225.3553   $225.36   $225.35   $225.40  
  Purchase #7 $144.25   7.811%   $155.5174   $155.52   $155.50   $155.50  
  7 purchase totals = $981.88       $1,060.0458   $1,060.06   $1,060.05   $1,060.00