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 $96.35   8.201%   $104.2517   $104.25   $104.25   $104.30  
  Purchase #2 $176.57   8.666%   $191.8716   $191.87   $191.85   $191.90  
  Purchase #3 $189.78   9.482%   $207.7749   $207.77   $207.75   $207.80  
  Purchase #4 $88.37   12.233%   $99.1803   $99.18   $99.20   $99.20  
  Purchase #5 $249.91   8.571%   $271.3298   $271.33   $271.35   $271.30  
  Purchase #6 $162.65   4.612%   $170.1514   $170.15   $170.15   $170.20  
  Purchase #7 $62.94   7.492%   $67.6555   $67.66   $67.65   $67.70  
  7 purchase totals = $1,026.57       $1,112.2152   $1,112.21   $1,112.20   $1,112.40