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 $247.69   8.107%   $267.7702   $267.77   $267.75   $267.80  
  Purchase #2 $238.28   11.618%   $265.9634   $265.96   $265.95   $266.00  
  Purchase #3 $112.30   13.566%   $127.5346   $127.53   $127.55   $127.50  
  Purchase #4 $147.57   13.341%   $167.2573   $167.26   $167.25   $167.30  
  Purchase #5 $128.30   4.398%   $133.9426   $133.94   $133.95   $133.90  
  Purchase #6 $231.84   13.694%   $263.5882   $263.59   $263.60   $263.60  
  Purchase #7 $16.74   5.810%   $17.7126   $17.71   $17.70   $17.70  
  7 purchase totals = $1,122.72       $1,243.7689   $1,243.76   $1,243.75   $1,243.80