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 $238.85   12.658%   $269.0836   $269.08   $269.10   $269.10  
  Purchase #2 $99.94   6.402%   $106.3382   $106.34   $106.35   $106.30  
  Purchase #3 $174.62   5.120%   $183.5605   $183.56   $183.55   $183.60  
  Purchase #4 $236.42   11.452%   $263.4948   $263.49   $263.50   $263.50  
  Purchase #5 $247.51   11.692%   $276.4489   $276.45   $276.45   $276.40  
  Purchase #6 $181.59   10.530%   $200.7114   $200.71   $200.70   $200.70  
  Purchase #7 $23.79   12.873%   $26.8525   $26.85   $26.85   $26.90  
  7 purchase totals = $1,202.72       $1,326.4899   $1,326.48   $1,326.50   $1,326.50