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 $249.37   8.751%   $271.1924   $271.19   $271.20   $271.20  
  Purchase #2 $144.36   3.717%   $149.7259   $149.73   $149.75   $149.70  
  Purchase #3 $55.83   10.520%   $61.7033   $61.70   $61.70   $61.70  
  Purchase #4 $240.84   6.566%   $256.6536   $256.65   $256.65   $256.70  
  Purchase #5 $67.82   9.805%   $74.4698   $74.47   $74.45   $74.50  
  Purchase #6 $31.96   3.605%   $33.1122   $33.11   $33.10   $33.10  
  Purchase #7 $246.25   4.196%   $256.5827   $256.58   $256.60   $256.60  
  7 purchase totals = $1,036.43       $1,103.4399   $1,103.43   $1,103.45   $1,103.50