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 $71.39   11.492%   $79.5941   $79.59   $79.60   $79.60  
  Purchase #2 $96.79   8.374%   $104.8952   $104.90   $104.90   $104.90  
  Purchase #3 $240.91   3.413%   $249.1323   $249.13   $249.15   $249.10  
  Purchase #4 $214.42   5.294%   $225.7714   $225.77   $225.75   $225.80  
  Purchase #5 $30.45   3.630%   $31.5553   $31.56   $31.55   $31.60  
  Purchase #6 $246.86   10.485%   $272.7433   $272.74   $272.75   $272.70  
  Purchase #7 $83.95   12.874%   $94.7577   $94.76   $94.75   $94.80  
  7 purchase totals = $984.77       $1,058.4493   $1,058.45   $1,058.45   $1,058.50