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 $120.97   8.567%   $131.3335   $131.33   $131.35   $131.30  
  Purchase #2 $181.38   12.634%   $204.2955   $204.30   $204.30   $204.30  
  Purchase #3 $35.45   3.372%   $36.6454   $36.65   $36.65   $36.60  
  Purchase #4 $191.57   3.724%   $198.7041   $198.70   $198.70   $198.70  
  Purchase #5 $15.81   6.662%   $16.8633   $16.86   $16.85   $16.90  
  Purchase #6 $94.59   10.247%   $104.2826   $104.28   $104.30   $104.30  
  Purchase #7 $215.41   8.551%   $233.8297   $233.83   $233.85   $233.80  
  7 purchase totals = $855.18       $925.9541   $925.95   $926.00   $925.90