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 $35.81   7.689%   $38.5634   $38.56   $38.55   $38.60  
  Purchase #2 $154.53   12.849%   $174.3856   $174.39   $174.40   $174.40  
  Purchase #3 $230.90   7.315%   $247.7903   $247.79   $247.80   $247.80  
  Purchase #4 $150.39   11.741%   $168.0473   $168.05   $168.05   $168.00  
  Purchase #5 $195.64   3.119%   $201.742   $201.74   $201.75   $201.70  
  Purchase #6 $95.75   13.388%   $108.569   $108.57   $108.55   $108.60  
  Purchase #7 $134.29   4.796%   $140.7305   $140.73   $140.75   $140.70  
  7 purchase totals = $997.31       $1,079.8281   $1,079.83   $1,079.85   $1,079.80