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 $147.44   12.331%   $165.6208   $165.62   $165.60   $165.60  
  Purchase #2 $16.67   4.195%   $17.3693   $17.37   $17.35   $17.40  
  Purchase #3 $183.40   8.312%   $198.6442   $198.64   $198.65   $198.60  
  Purchase #4 $55.57   12.783%   $62.6735   $62.67   $62.65   $62.70  
  Purchase #5 $49.85   6.282%   $52.9816   $52.98   $53.00   $53.00  
  Purchase #6 $232.55   11.624%   $259.5816   $259.58   $259.60   $259.60  
  Purchase #7 $210.45   4.833%   $220.621   $220.62   $220.60   $220.60  
  7 purchase totals = $895.93       $977.4920   $977.48   $977.45   $977.50