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 $149.49   11.776%   $167.0939   $167.09   $167.10   $167.10  
  Purchase #2 $233.48   4.201%   $243.2885   $243.29   $243.30   $243.30  
  Purchase #3 $174.26   7.806%   $187.8627   $187.86   $187.85   $187.90  
  Purchase #4 $108.43   6.513%   $115.492   $115.49   $115.50   $115.50  
  Purchase #5 $139.26   12.626%   $156.843   $156.84   $156.85   $156.80  
  Purchase #6 $173.80   7.111%   $186.1589   $186.16   $186.15   $186.20  
  Purchase #7 $38.86   4.317%   $40.5376   $40.54   $40.55   $40.50  
  7 purchase totals = $1,017.58       $1,097.2766   $1,097.27   $1,097.30   $1,097.30