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 $39.68   8.641%   $43.1087   $43.11   $43.10   $43.10  
  Purchase #2 $80.63   9.183%   $88.0343   $88.03   $88.05   $88.00  
  Purchase #3 $66.98   8.426%   $72.6237   $72.62   $72.60   $72.60  
  Purchase #4 $179.33   12.418%   $201.5992   $201.60   $201.60   $201.60  
  Purchase #5 $53.72   11.516%   $59.9064   $59.91   $59.90   $59.90  
  Purchase #6 $250.26   13.283%   $283.502   $283.50   $283.50   $283.50  
  Purchase #7 $103.88   13.739%   $118.1521   $118.15   $118.15   $118.20  
  7 purchase totals = $774.48       $866.9264   $866.92   $866.90   $866.90