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 $42.71   8.379%   $46.2887   $46.29   $46.30   $46.30  
  Purchase #2 $191.54   4.760%   $200.6573   $200.66   $200.65   $200.70  
  Purchase #3 $94.77   3.562%   $98.1457   $98.15   $98.15   $98.10  
  Purchase #4 $218.38   7.372%   $234.479   $234.48   $234.50   $234.50  
  Purchase #5 $118.47   11.361%   $131.9294   $131.93   $131.95   $131.90  
  Purchase #6 $166.75   8.652%   $181.1772   $181.18   $181.20   $181.20  
  Purchase #7 $169.90   4.611%   $177.7341   $177.73   $177.75   $177.70  
  7 purchase totals = $1,002.52       $1,070.4114   $1,070.42   $1,070.50   $1,070.40