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 $67.76   12.648%   $76.3303   $76.33   $76.35   $76.30  
  Purchase #2 $198.77   6.505%   $211.7   $211.70   $211.70   $211.70  
  Purchase #3 $242.55   6.357%   $257.9689   $257.97   $257.95   $258.00  
  Purchase #4 $20.73   11.844%   $23.1853   $23.19   $23.20   $23.20  
  Purchase #5 $9.26   4.474%   $9.6743   $9.67   $9.65   $9.70  
  Purchase #6 $223.50   5.612%   $236.0428   $236.04   $236.05   $236.00  
  Purchase #7 $186.77   9.127%   $203.8165   $203.82   $203.80   $203.80  
  7 purchase totals = $949.34       $1,018.7181   $1,018.72   $1,018.70   $1,018.70