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 $92.53   4.546%   $96.7364   $96.74   $96.75   $96.70  
  Purchase #2 $228.92   11.782%   $255.8914   $255.89   $255.90   $255.90  
  Purchase #3 $14.40   3.349%   $14.8823   $14.88   $14.90   $14.90  
  Purchase #4 $28.58   4.616%   $29.8993   $29.90   $29.90   $29.90  
  Purchase #5 $189.96   6.701%   $202.6892   $202.69   $202.70   $202.70  
  Purchase #6 $94.73   12.556%   $106.6243   $106.62   $106.60   $106.60  
  Purchase #7 $34.28   11.265%   $38.1416   $38.14   $38.15   $38.10  
  7 purchase totals = $683.40       $744.8645   $744.86   $744.90   $744.80