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 $104.82   8.491%   $113.7203   $113.72   $113.70   $113.70  
  Purchase #2 $211.59   13.677%   $240.5292   $240.53   $240.55   $240.50  
  Purchase #3 $159.98   10.477%   $176.7411   $176.74   $176.75   $176.70  
  Purchase #4 $207.43   7.518%   $223.0246   $223.02   $223.00   $223.00  
  Purchase #5 $69.98   8.567%   $75.9752   $75.98   $76.00   $76.00  
  Purchase #6 $32.60   12.593%   $36.7053   $36.71   $36.70   $36.70  
  Purchase #7 $238.66   3.333%   $246.6145   $246.61   $246.60   $246.60  
  7 purchase totals = $1,025.06       $1,113.3102   $1,113.31   $1,113.30   $1,113.20