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 $118.36   13.236%   $134.0261   $134.03   $134.05   $134.00  
  Purchase #2 $130.85   7.553%   $140.7331   $140.73   $140.75   $140.70  
  Purchase #3 $212.94   6.221%   $226.187   $226.19   $226.20   $226.20  
  Purchase #4 $94.90   3.227%   $97.9624   $97.96   $97.95   $98.00  
  Purchase #5 $208.45   11.234%   $231.8673   $231.87   $231.85   $231.90  
  Purchase #6 $60.84   10.192%   $67.0408   $67.04   $67.05   $67.00  
  Purchase #7 $142.48   8.585%   $154.7119   $154.71   $154.70   $154.70  
  7 purchase totals = $968.82       $1,052.5286   $1,052.53   $1,052.55   $1,052.50