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 $237.64   11.427%   $264.7951   $264.80   $264.80   $264.80  
  Purchase #2 $98.89   12.227%   $110.9813   $110.98   $111.00   $111.00  
  Purchase #3 $104.61   10.260%   $115.343   $115.34   $115.35   $115.30  
  Purchase #4 $175.61   10.222%   $193.5609   $193.56   $193.55   $193.60  
  Purchase #5 $117.48   10.129%   $129.3795   $129.38   $129.40   $129.40  
  Purchase #6 $111.85   7.313%   $120.0296   $120.03   $120.05   $120.00  
  Purchase #7 $113.99   7.543%   $122.5883   $122.59   $122.60   $122.60  
  7 purchase totals = $960.07       $1,056.6777   $1,056.68   $1,056.75   $1,056.70