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 $68.78   11.793%   $76.8912   $76.89   $76.90   $76.90  
  Purchase #2 $180.91   8.118%   $195.5963   $195.60   $195.60   $195.60  
  Purchase #3 $241.73   7.822%   $260.6381   $260.64   $260.65   $260.60  
  Purchase #4 $116.50   13.482%   $132.2065   $132.21   $132.20   $132.20  
  Purchase #5 $11.35   3.371%   $11.7326   $11.73   $11.75   $11.70  
  Purchase #6 $136.78   9.652%   $149.982   $149.98   $150.00   $150.00  
  Purchase #7 $148.78   12.718%   $167.7018   $167.70   $167.70   $167.70  
  7 purchase totals = $904.83       $994.7485   $994.75   $994.80   $994.70