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 $31.65   12.437%   $35.5863   $35.59   $35.60   $35.60  
  Purchase #2 $164.35   10.499%   $181.6051   $181.61   $181.60   $181.60  
  Purchase #3 $64.33   11.707%   $71.8611   $71.86   $71.85   $71.90  
  Purchase #4 $81.82   3.658%   $84.813   $84.81   $84.80   $84.80  
  Purchase #5 $102.70   12.373%   $115.4071   $115.41   $115.40   $115.40  
  Purchase #6 $90.68   4.393%   $94.6636   $94.66   $94.65   $94.70  
  Purchase #7 $155.52   4.628%   $162.7175   $162.72   $162.70   $162.70  
  7 purchase totals = $691.05       $746.6537   $746.66   $746.60   $746.70