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 $67.73   11.856%   $75.7601   $75.76   $75.75   $75.80  
  Purchase #2 $88.97   4.596%   $93.0591   $93.06   $93.05   $93.10  
  Purchase #3 $204.74   5.194%   $215.3742   $215.37   $215.35   $215.40  
  Purchase #4 $223.75   7.583%   $240.717   $240.72   $240.70   $240.70  
  Purchase #5 $113.86   3.192%   $117.4944   $117.49   $117.50   $117.50  
  Purchase #6 $101.55   3.669%   $105.2759   $105.28   $105.30   $105.30  
  Purchase #7 $250.71   7.209%   $268.7837   $268.78   $268.80   $268.80  
  7 purchase totals = $1,051.31       $1,116.4644   $1,116.46   $1,116.45   $1,116.60