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 $208.56   9.526%   $228.4274   $228.43   $228.45   $228.40  
  Purchase #2 $212.33   5.414%   $223.8255   $223.83   $223.85   $223.80  
  Purchase #3 $112.69   9.257%   $123.1217   $123.12   $123.10   $123.10  
  Purchase #4 $110.25   5.544%   $116.3623   $116.36   $116.35   $116.40  
  Purchase #5 $181.87   6.828%   $194.2881   $194.29   $194.30   $194.30  
  Purchase #6 $22.40   5.698%   $23.6764   $23.68   $23.70   $23.70  
  Purchase #7 $112.92   9.482%   $123.6271   $123.63   $123.65   $123.60  
  7 purchase totals = $961.02       $1,033.3285   $1,033.34   $1,033.40   $1,033.30