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 $111.99   5.834%   $118.5235   $118.52   $118.50   $118.50  
  Purchase #2 $225.41   7.398%   $242.0858   $242.09   $242.10   $242.10  
  Purchase #3 $205.26   11.730%   $229.337   $229.34   $229.35   $229.30  
  Purchase #4 $240.60   11.741%   $268.8488   $268.85   $268.85   $268.80  
  Purchase #5 $249.38   5.699%   $263.5922   $263.59   $263.60   $263.60  
  Purchase #6 $162.78   13.436%   $184.6511   $184.65   $184.65   $184.70  
  Purchase #7 $214.57   5.765%   $226.94   $226.94   $226.95   $226.90  
  7 purchase totals = $1,409.99       $1,533.9784   $1,533.98   $1,534.00   $1,533.90