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 $241.86   6.152%   $256.7392   $256.74   $256.75   $256.70  
  Purchase #2 $54.95   6.525%   $58.5355   $58.54   $58.55   $58.50  
  Purchase #3 $162.30   11.761%   $181.3881   $181.39   $181.40   $181.40  
  Purchase #4 $194.60   13.325%   $220.5305   $220.53   $220.55   $220.50  
  Purchase #5 $141.28   8.479%   $153.2591   $153.26   $153.25   $153.30  
  Purchase #6 $79.93   7.153%   $85.6474   $85.65   $85.65   $85.60  
  Purchase #7 $245.69   11.672%   $274.3669   $274.37   $274.35   $274.40  
  7 purchase totals = $1,120.61       $1,230.4667   $1,230.48   $1,230.50   $1,230.40