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 $81.89   13.486%   $92.9337   $92.93   $92.95   $92.90  
  Purchase #2 $180.25   7.407%   $193.6011   $193.60   $193.60   $193.60  
  Purchase #3 $244.39   13.288%   $276.8645   $276.86   $276.85   $276.90  
  Purchase #4 $90.52   5.503%   $95.5013   $95.50   $95.50   $95.50  
  Purchase #5 $123.64   8.411%   $134.0394   $134.04   $134.05   $134.00  
  Purchase #6 $245.91   11.173%   $273.3855   $273.39   $273.40   $273.40  
  Purchase #7 $230.40   11.616%   $257.1633   $257.16   $257.15   $257.20  
  7 purchase totals = $1,197.00       $1,323.4888   $1,323.48   $1,323.50   $1,323.50