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 $29.58   13.799%   $33.6617   $33.66   $33.65   $33.70  
  Purchase #2 $165.82   13.173%   $187.6635   $187.66   $187.65   $187.70  
  Purchase #3 $135.55   8.310%   $146.8142   $146.81   $146.80   $146.80  
  Purchase #4 $222.74   10.334%   $245.758   $245.76   $245.75   $245.80  
  Purchase #5 $84.74   6.319%   $90.0947   $90.09   $90.10   $90.10  
  Purchase #6 $99.98   10.509%   $110.4869   $110.49   $110.50   $110.50  
  Purchase #7 $201.53   9.453%   $220.5806   $220.58   $220.60   $220.60  
  7 purchase totals = $939.94       $1,035.0596   $1,035.05   $1,035.05   $1,035.20