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 $147.32   6.219%   $156.4818   $156.48   $156.50   $156.50  
  Purchase #2 $43.31   6.628%   $46.1806   $46.18   $46.20   $46.20  
  Purchase #3 $244.80   5.468%   $258.1857   $258.19   $258.20   $258.20  
  Purchase #4 $96.70   6.616%   $103.0977   $103.10   $103.10   $103.10  
  Purchase #5 $51.92   5.668%   $54.8628   $54.86   $54.85   $54.90  
  Purchase #6 $73.37   10.314%   $80.9374   $80.94   $80.95   $80.90  
  Purchase #7 $125.99   5.720%   $133.1966   $133.20   $133.20   $133.20  
  7 purchase totals = $783.41       $832.9426   $832.95   $833.00   $833.00