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 $66.79   12.662%   $75.2469   $75.25   $75.25   $75.20  
  Purchase #2 $235.40   5.634%   $248.6624   $248.66   $248.65   $248.70  
  Purchase #3 $239.30   13.459%   $271.5074   $271.51   $271.50   $271.50  
  Purchase #4 $235.57   11.623%   $262.9503   $262.95   $262.95   $263.00  
  Purchase #5 $168.97   6.170%   $179.3954   $179.40   $179.40   $179.40  
  Purchase #6 $130.83   13.650%   $148.6883   $148.69   $148.70   $148.70  
  Purchase #7 $179.33   4.865%   $188.0544   $188.05   $188.05   $188.10  
  7 purchase totals = $1,256.19       $1,374.5051   $1,374.51   $1,374.50   $1,374.60