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 $134.90   13.828%   $153.554   $153.55   $153.55   $153.60  
  Purchase #2 $23.68   3.767%   $24.572   $24.57   $24.55   $24.60  
  Purchase #3 $74.44   8.150%   $80.5069   $80.51   $80.50   $80.50  
  Purchase #4 $210.28   5.308%   $221.4417   $221.44   $221.45   $221.40  
  Purchase #5 $167.55   8.267%   $181.4014   $181.40   $181.40   $181.40  
  Purchase #6 $28.50   4.771%   $29.8597   $29.86   $29.85   $29.90  
  Purchase #7 $63.33   13.236%   $71.7124   $71.71   $71.70   $71.70  
  7 purchase totals = $702.68       $763.0481   $763.04   $763.00   $763.10