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 $248.34   11.181%   $276.1069   $276.11   $276.10   $276.10  
  Purchase #2 $149.51   13.854%   $170.2231   $170.22   $170.20   $170.20  
  Purchase #3 $108.87   12.553%   $122.5365   $122.54   $122.55   $122.50  
  Purchase #4 $159.91   11.190%   $177.8039   $177.80   $177.80   $177.80  
  Purchase #5 $124.84   10.708%   $138.2079   $138.21   $138.20   $138.20  
  Purchase #6 $204.32   10.586%   $225.9493   $225.95   $225.95   $225.90  
  Purchase #7 $23.76   11.532%   $26.5   $26.50   $26.50   $26.50  
  7 purchase totals = $1,019.55       $1,137.3276   $1,137.33   $1,137.30   $1,137.20