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 $244.56   6.624%   $260.7597   $260.76   $260.75   $260.80  
  Purchase #2 $77.33   5.145%   $81.3086   $81.31   $81.30   $81.30  
  Purchase #3 $100.31   13.517%   $113.8689   $113.87   $113.85   $113.90  
  Purchase #4 $213.60   9.422%   $233.7254   $233.73   $233.75   $233.70  
  Purchase #5 $116.67   3.351%   $120.5796   $120.58   $120.60   $120.60  
  Purchase #6 $203.73   8.180%   $220.3951   $220.40   $220.40   $220.40  
  Purchase #7 $41.56   6.213%   $44.1421   $44.14   $44.15   $44.10  
  7 purchase totals = $997.76       $1,074.7794   $1,074.79   $1,074.80   $1,074.80