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 $158.67   10.544%   $175.4002   $175.40   $175.40   $175.40  
  Purchase #2 $203.41   3.169%   $209.8561   $209.86   $209.85   $209.90  
  Purchase #3 $155.73   6.441%   $165.7606   $165.76   $165.75   $165.80  
  Purchase #4 $190.96   8.238%   $206.6913   $206.69   $206.70   $206.70  
  Purchase #5 $23.63   5.801%   $25.0008   $25.00   $25.00   $25.00  
  Purchase #6 $24.58   5.607%   $25.9582   $25.96   $25.95   $26.00  
  Purchase #7 $129.61   12.285%   $145.5326   $145.53   $145.55   $145.50  
  7 purchase totals = $886.59       $954.1998   $954.20   $954.20   $954.30