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 $33.48   3.806%   $34.7542   $34.75   $34.75   $34.80  
  Purchase #2 $165.93   4.421%   $173.2658   $173.27   $173.25   $173.30  
  Purchase #3 $75.47   7.208%   $80.9099   $80.91   $80.90   $80.90  
  Purchase #4 $143.44   12.286%   $161.063   $161.06   $161.05   $161.10  
  Purchase #5 $171.36   11.392%   $190.8813   $190.88   $190.90   $190.90  
  Purchase #6 $146.90   3.678%   $152.303   $152.30   $152.30   $152.30  
  Purchase #7 $242.53   11.546%   $270.5325   $270.53   $270.55   $270.50  
  7 purchase totals = $979.11       $1,063.7097   $1,063.70   $1,063.70   $1,063.80