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 $147.86   10.776%   $163.7934   $163.79   $163.80   $163.80  
  Purchase #2 $223.41   13.407%   $253.3626   $253.36   $253.35   $253.40  
  Purchase #3 $157.74   4.771%   $165.2658   $165.27   $165.25   $165.30  
  Purchase #4 $7.35   5.126%   $7.7268   $7.73   $7.75   $7.70  
  Purchase #5 $99.48   4.422%   $103.879   $103.88   $103.90   $103.90  
  Purchase #6 $48.57   9.380%   $53.1259   $53.13   $53.15   $53.10  
  Purchase #7 $20.85   13.437%   $23.6516   $23.65   $23.65   $23.70  
  7 purchase totals = $705.26       $770.8051   $770.81   $770.85   $770.90