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 $85.45   13.754%   $97.2028   $97.20   $97.20   $97.20  
  Purchase #2 $10.73   3.811%   $11.1389   $11.14   $11.15   $11.10  
  Purchase #3 $203.67   13.708%   $231.5891   $231.59   $231.60   $231.60  
  Purchase #4 $213.48   7.608%   $229.7216   $229.72   $229.70   $229.70  
  Purchase #5 $249.61   9.200%   $272.5741   $272.57   $272.55   $272.60  
  Purchase #6 $111.73   4.549%   $116.8126   $116.81   $116.80   $116.80  
  Purchase #7 $9.44   6.121%   $10.0178   $10.02   $10.00   $10.00  
  7 purchase totals = $884.11       $969.0569   $969.05   $969.00   $969.00