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 $176.51   11.174%   $196.2332   $196.23   $196.25   $196.20  
  Purchase #2 $10.76   9.366%   $11.7678   $11.77   $11.75   $11.80  
  Purchase #3 $117.55   13.712%   $133.6685   $133.67   $133.65   $133.70  
  Purchase #4 $196.28   6.763%   $209.5544   $209.55   $209.55   $209.60  
  Purchase #5 $245.55   6.187%   $260.7422   $260.74   $260.75   $260.70  
  Purchase #6 $98.51   9.849%   $108.2122   $108.21   $108.20   $108.20  
  Purchase #7 $79.53   11.649%   $88.7944   $88.79   $88.80   $88.80  
  7 purchase totals = $924.69       $1,008.9727   $1,008.96   $1,008.95   $1,009.00