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 $106.29   12.383%   $119.4519   $119.45   $119.45   $119.50  
  Purchase #2 $240.67   6.323%   $255.8876   $255.89   $255.90   $255.90  
  Purchase #3 $233.85   12.263%   $262.527   $262.53   $262.55   $262.50  
  Purchase #4 $86.67   5.460%   $91.4022   $91.40   $91.40   $91.40  
  Purchase #5 $13.52   7.737%   $14.566   $14.57   $14.55   $14.60  
  Purchase #6 $201.97   13.189%   $228.6078   $228.61   $228.60   $228.60  
  Purchase #7 $75.34   11.762%   $84.2015   $84.20   $84.20   $84.20  
  7 purchase totals = $958.31       $1,056.6440   $1,056.65   $1,056.65   $1,056.70