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 $52.53   11.629%   $58.6387   $58.64   $58.65   $58.60  
  Purchase #2 $249.55   8.338%   $270.3575   $270.36   $270.35   $270.40  
  Purchase #3 $59.38   10.675%   $65.7188   $65.72   $65.70   $65.70  
  Purchase #4 $82.37   12.621%   $92.7659   $92.77   $92.75   $92.80  
  Purchase #5 $35.46   10.345%   $39.1283   $39.13   $39.15   $39.10  
  Purchase #6 $250.85   12.825%   $283.0215   $283.02   $283.00   $283.00  
  Purchase #7 $235.25   10.500%   $259.9513   $259.95   $259.95   $260.00  
  7 purchase totals = $965.39       $1,069.5820   $1,069.59   $1,069.55   $1,069.60