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 $106.56   6.702%   $113.7017   $113.70   $113.70   $113.70  
  Purchase #2 $196.97   13.651%   $223.8584   $223.86   $223.85   $223.90  
  Purchase #3 $116.84   6.790%   $124.7734   $124.77   $124.75   $124.80  
  Purchase #4 $203.75   12.351%   $228.9152   $228.92   $228.90   $228.90  
  Purchase #5 $182.67   13.226%   $206.8299   $206.83   $206.85   $206.80  
  Purchase #6 $90.55   8.368%   $98.1272   $98.13   $98.15   $98.10  
  Purchase #7 $116.73   11.667%   $130.3489   $130.35   $130.35   $130.30  
  7 purchase totals = $1,014.07       $1,126.5547   $1,126.56   $1,126.55   $1,126.50