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 $203.48   10.596%   $225.0407   $225.04   $225.05   $225.00  
  Purchase #2 $188.60   13.822%   $214.6683   $214.67   $214.65   $214.70  
  Purchase #3 $126.76   4.690%   $132.705   $132.71   $132.70   $132.70  
  Purchase #4 $87.40   4.654%   $91.4676   $91.47   $91.45   $91.50  
  Purchase #5 $127.51   7.692%   $137.3181   $137.32   $137.30   $137.30  
  Purchase #6 $179.55   5.522%   $189.4648   $189.46   $189.45   $189.50  
  Purchase #7 $120.35   11.491%   $134.1794   $134.18   $134.20   $134.20  
  7 purchase totals = $1,033.65       $1,124.8439   $1,124.85   $1,124.80   $1,124.90