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 $169.33   10.590%   $187.262   $187.26   $187.25   $187.30  
  Purchase #2 $29.82   5.516%   $31.4649   $31.46   $31.45   $31.50  
  Purchase #3 $148.36   13.577%   $168.5028   $168.50   $168.50   $168.50  
  Purchase #4 $227.99   5.177%   $239.793   $239.79   $239.80   $239.80  
  Purchase #5 $40.85   7.814%   $44.042   $44.04   $44.05   $44.00  
  Purchase #6 $198.55   5.356%   $209.1843   $209.18   $209.20   $209.20  
  Purchase #7 $134.73   5.496%   $142.1348   $142.13   $142.15   $142.10  
  7 purchase totals = $949.63       $1,022.3838   $1,022.36   $1,022.40   $1,022.40