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 $66.58   4.456%   $69.5468   $69.55   $69.55   $69.50  
  Purchase #2 $60.33   10.477%   $66.6508   $66.65   $66.65   $66.70  
  Purchase #3 $131.78   4.569%   $137.801   $137.80   $137.80   $137.80  
  Purchase #4 $227.28   7.126%   $243.476   $243.48   $243.50   $243.50  
  Purchase #5 $98.84   7.472%   $106.2253   $106.23   $106.25   $106.20  
  Purchase #6 $94.56   4.838%   $99.1348   $99.13   $99.15   $99.10  
  Purchase #7 $240.30   7.462%   $258.2312   $258.23   $258.25   $258.20  
  7 purchase totals = $919.67       $981.0659   $981.07   $981.15   $981.00