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 $243.63   4.237%   $253.9526   $253.95   $253.95   $254.00  
  Purchase #2 $180.55   3.379%   $186.6508   $186.65   $186.65   $186.70  
  Purchase #3 $50.51   3.826%   $52.4425   $52.44   $52.45   $52.40  
  Purchase #4 $179.85   11.466%   $200.4716   $200.47   $200.45   $200.50  
  Purchase #5 $221.57   5.176%   $233.0385   $233.04   $233.05   $233.00  
  Purchase #6 $167.29   9.672%   $183.4703   $183.47   $183.45   $183.50  
  Purchase #7 $58.98   10.832%   $65.3687   $65.37   $65.35   $65.40  
  7 purchase totals = $1,102.38       $1,175.3950   $1,175.39   $1,175.35   $1,175.50