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 $202.45   11.651%   $226.0374   $226.04   $226.05   $226.00  
  Purchase #2 $178.45   10.494%   $197.1765   $197.18   $197.20   $197.20  
  Purchase #3 $118.65   4.823%   $124.3725   $124.37   $124.35   $124.40  
  Purchase #4 $102.32   6.371%   $108.8388   $108.84   $108.85   $108.80  
  Purchase #5 $175.92   9.375%   $192.4125   $192.41   $192.40   $192.40  
  Purchase #6 $242.74   7.478%   $260.8921   $260.89   $260.90   $260.90  
  Purchase #7 $25.26   5.123%   $26.5541   $26.55   $26.55   $26.60  
  7 purchase totals = $1,045.79       $1,136.2839   $1,136.28   $1,136.30   $1,136.30