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 $113.99   8.814%   $124.0371   $124.04   $124.05   $124.00  
  Purchase #2 $227.48   8.146%   $246.0105   $246.01   $246.00   $246.00  
  Purchase #3 $15.37   7.838%   $16.5747   $16.57   $16.55   $16.60  
  Purchase #4 $61.33   7.566%   $65.9702   $65.97   $65.95   $66.00  
  Purchase #5 $121.44   6.814%   $129.7149   $129.71   $129.70   $129.70  
  Purchase #6 $49.47   13.131%   $55.9659   $55.97   $55.95   $56.00  
  Purchase #7 $108.94   13.371%   $123.5064   $123.51   $123.50   $123.50  
  7 purchase totals = $698.02       $761.7797   $761.78   $761.70   $761.80