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 $234.28   5.763%   $247.7816   $247.78   $247.80   $247.80  
  Purchase #2 $133.58   6.484%   $142.2413   $142.24   $142.25   $142.20  
  Purchase #3 $218.25   9.782%   $239.5992   $239.60   $239.60   $239.60  
  Purchase #4 $104.81   5.339%   $110.4058   $110.41   $110.40   $110.40  
  Purchase #5 $68.33   7.810%   $73.6666   $73.67   $73.65   $73.70  
  Purchase #6 $5.74   5.862%   $6.0765   $6.08   $6.10   $6.10  
  Purchase #7 $229.53   6.373%   $244.1579   $244.16   $244.15   $244.20  
  7 purchase totals = $994.52       $1,063.9289   $1,063.94   $1,063.95   $1,064.00