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 $201.94   12.215%   $226.607   $226.61   $226.60   $226.60  
  Purchase #2 $191.79   7.373%   $205.9307   $205.93   $205.95   $205.90  
  Purchase #3 $83.35   7.352%   $89.4779   $89.48   $89.50   $89.50  
  Purchase #4 $75.38   11.124%   $83.7653   $83.77   $83.75   $83.80  
  Purchase #5 $171.86   3.741%   $178.2893   $178.29   $178.30   $178.30  
  Purchase #6 $179.45   10.120%   $197.6103   $197.61   $197.60   $197.60  
  Purchase #7 $56.89   10.750%   $63.0057   $63.01   $63.00   $63.00  
  7 purchase totals = $960.66       $1,044.6862   $1,044.70   $1,044.70   $1,044.70