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 $22.62   9.642%   $24.801   $24.80   $24.80   $24.80  
  Purchase #2 $229.34   12.557%   $258.1382   $258.14   $258.15   $258.10  
  Purchase #3 $120.80   8.682%   $131.2879   $131.29   $131.30   $131.30  
  Purchase #4 $241.74   5.193%   $254.2936   $254.29   $254.30   $254.30  
  Purchase #5 $236.29   4.698%   $247.3909   $247.39   $247.40   $247.40  
  Purchase #6 $143.25   7.415%   $153.872   $153.87   $153.85   $153.90  
  Purchase #7 $95.97   5.348%   $101.1025   $101.10   $101.10   $101.10  
  7 purchase totals = $1,090.01       $1,170.8861   $1,170.88   $1,170.90   $1,170.90