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 $112.94   10.627%   $124.9421   $124.94   $124.95   $124.90  
  Purchase #2 $7.79   7.167%   $8.3483   $8.35   $8.35   $8.30  
  Purchase #3 $31.62   11.548%   $35.2715   $35.27   $35.25   $35.30  
  Purchase #4 $40.48   7.738%   $43.6123   $43.61   $43.60   $43.60  
  Purchase #5 $243.51   8.720%   $264.7441   $264.74   $264.75   $264.70  
  Purchase #6 $185.64   9.452%   $203.1867   $203.19   $203.20   $203.20  
  Purchase #7 $211.56   5.666%   $223.547   $223.55   $223.55   $223.50  
  7 purchase totals = $833.54       $903.6520   $903.65   $903.65   $903.50