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 $37.98   8.726%   $41.2941   $41.29   $41.30   $41.30  
  Purchase #2 $214.75   8.378%   $232.7418   $232.74   $232.75   $232.70  
  Purchase #3 $118.31   5.184%   $124.4432   $124.44   $124.45   $124.40  
  Purchase #4 $220.88   10.460%   $243.984   $243.98   $244.00   $244.00  
  Purchase #5 $165.71   13.540%   $188.1471   $188.15   $188.15   $188.10  
  Purchase #6 $227.39   6.201%   $241.4905   $241.49   $241.50   $241.50  
  Purchase #7 $112.89   12.135%   $126.5892   $126.59   $126.60   $126.60  
  7 purchase totals = $1,097.91       $1,198.6899   $1,198.68   $1,198.75   $1,198.60