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 $239.45   9.827%   $262.9808   $262.98   $263.00   $263.00  
  Purchase #2 $23.82   11.858%   $26.6446   $26.64   $26.65   $26.60  
  Purchase #3 $145.96   13.628%   $165.8514   $165.85   $165.85   $165.90  
  Purchase #4 $244.87   3.517%   $253.4821   $253.48   $253.50   $253.50  
  Purchase #5 $212.27   12.144%   $238.0481   $238.05   $238.05   $238.00  
  Purchase #6 $200.49   6.857%   $214.2376   $214.24   $214.25   $214.20  
  Purchase #7 $126.25   5.788%   $133.5574   $133.56   $133.55   $133.60  
  7 purchase totals = $1,193.11       $1,294.8020   $1,294.80   $1,294.85   $1,294.80