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 $61.25   6.582%   $65.2815   $65.28   $65.30   $65.30  
  Purchase #2 $99.80   9.539%   $109.3199   $109.32   $109.30   $109.30  
  Purchase #3 $66.25   5.715%   $70.0362   $70.04   $70.05   $70.00  
  Purchase #4 $123.84   11.628%   $138.2401   $138.24   $138.25   $138.20  
  Purchase #5 $94.43   8.334%   $102.2998   $102.30   $102.30   $102.30  
  Purchase #6 $68.57   5.700%   $72.4785   $72.48   $72.50   $72.50  
  Purchase #7 $192.89   11.111%   $214.322   $214.32   $214.30   $214.30  
  7 purchase totals = $707.03       $771.9780   $771.98   $772.00   $771.90