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 $24.40   9.577%   $26.7368   $26.74   $26.75   $26.70  
  Purchase #2 $58.42   10.806%   $64.7329   $64.73   $64.75   $64.70  
  Purchase #3 $180.73   5.331%   $190.3647   $190.36   $190.35   $190.40  
  Purchase #4 $238.79   11.158%   $265.4342   $265.43   $265.45   $265.40  
  Purchase #5 $60.68   5.653%   $64.1102   $64.11   $64.10   $64.10  
  Purchase #6 $184.70   13.513%   $209.6585   $209.66   $209.65   $209.70  
  Purchase #7 $196.84   4.582%   $205.8592   $205.86   $205.85   $205.90  
  7 purchase totals = $944.56       $1,026.8965   $1,026.89   $1,026.90   $1,026.90