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 $200.33   9.224%   $218.8084   $218.81   $218.80   $218.80  
  Purchase #2 $184.25   3.862%   $191.3657   $191.37   $191.35   $191.40  
  Purchase #3 $43.53   8.247%   $47.1199   $47.12   $47.10   $47.10  
  Purchase #4 $68.61   13.688%   $78.0013   $78.00   $78.00   $78.00  
  Purchase #5 $163.65   5.776%   $173.1024   $173.10   $173.10   $173.10  
  Purchase #6 $60.65   10.799%   $67.1996   $67.20   $67.20   $67.20  
  Purchase #7 $223.79   5.594%   $236.3088   $236.31   $236.30   $236.30  
  7 purchase totals = $944.81       $1,011.9061   $1,011.91   $1,011.85   $1,011.90