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 $96.96   6.788%   $103.5416   $103.54   $103.55   $103.50  
  Purchase #2 $246.92   12.392%   $277.5183   $277.52   $277.50   $277.50  
  Purchase #3 $14.76   8.523%   $16.018   $16.02   $16.00   $16.00  
  Purchase #4 $38.73   13.662%   $44.0213   $44.02   $44.00   $44.00  
  Purchase #5 $133.77   12.449%   $150.423   $150.42   $150.40   $150.40  
  Purchase #6 $214.68   9.168%   $234.3619   $234.36   $234.35   $234.40  
  Purchase #7 $131.44   9.222%   $143.5614   $143.56   $143.55   $143.60  
  7 purchase totals = $877.26       $969.4455   $969.44   $969.35   $969.40