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 $216.75   13.790%   $246.6398   $246.64   $246.65   $246.60  
  Purchase #2 $138.25   10.803%   $153.1851   $153.19   $153.20   $153.20  
  Purchase #3 $118.52   5.181%   $124.6605   $124.66   $124.65   $124.70  
  Purchase #4 $46.57   5.683%   $49.2166   $49.22   $49.20   $49.20  
  Purchase #5 $59.55   13.205%   $67.4136   $67.41   $67.40   $67.40  
  Purchase #6 $80.56   10.866%   $89.3136   $89.31   $89.30   $89.30  
  Purchase #7 $185.62   7.339%   $199.2427   $199.24   $199.25   $199.20  
  7 purchase totals = $845.82       $929.6719   $929.67   $929.65   $929.60