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 $148.54   11.707%   $165.9296   $165.93   $165.95   $165.90  
  Purchase #2 $100.51   4.333%   $104.8651   $104.87   $104.85   $104.90  
  Purchase #3 $206.39   4.685%   $216.0594   $216.06   $216.05   $216.10  
  Purchase #4 $150.48   12.448%   $169.2118   $169.21   $169.20   $169.20  
  Purchase #5 $182.64   4.433%   $190.7364   $190.74   $190.75   $190.70  
  Purchase #6 $141.45   12.755%   $159.4919   $159.49   $159.50   $159.50  
  Purchase #7 $43.70   13.725%   $49.6978   $49.70   $49.70   $49.70  
  7 purchase totals = $973.71       $1,055.9920   $1,056.00   $1,056.00   $1,056.00