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 $67.65   13.594%   $76.8463   $76.85   $76.85   $76.80  
  Purchase #2 $80.85   6.253%   $85.9056   $85.91   $85.90   $85.90  
  Purchase #3 $158.93   9.614%   $174.2095   $174.21   $174.20   $174.20  
  Purchase #4 $68.98   10.308%   $76.0905   $76.09   $76.10   $76.10  
  Purchase #5 $22.46   5.729%   $23.7467   $23.75   $23.75   $23.70  
  Purchase #6 $108.94   6.581%   $116.1093   $116.11   $116.10   $116.10  
  Purchase #7 $50.79   10.323%   $56.0331   $56.03   $56.05   $56.00  
  7 purchase totals = $558.60       $608.9410   $608.95   $608.95   $608.80