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 $59.50   10.572%   $65.7903   $65.79   $65.80   $65.80  
  Purchase #2 $247.81   12.315%   $278.3278   $278.33   $278.35   $278.30  
  Purchase #3 $213.34   13.448%   $242.03   $242.03   $242.05   $242.00  
  Purchase #4 $135.66   13.116%   $153.4532   $153.45   $153.45   $153.50  
  Purchase #5 $182.90   11.536%   $203.9993   $204.00   $204.00   $204.00  
  Purchase #6 $161.48   3.323%   $166.846   $166.85   $166.85   $166.80  
  Purchase #7 $101.81   4.304%   $106.1919   $106.19   $106.20   $106.20  
  7 purchase totals = $1,102.50       $1,216.6385   $1,216.64   $1,216.70   $1,216.60