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 $64.33   10.774%   $71.2609   $71.26   $71.25   $71.30  
  Purchase #2 $175.94   9.562%   $192.7634   $192.76   $192.75   $192.80  
  Purchase #3 $82.77   5.870%   $87.6286   $87.63   $87.65   $87.60  
  Purchase #4 $191.96   5.494%   $202.5063   $202.51   $202.50   $202.50  
  Purchase #5 $244.40   4.706%   $255.9015   $255.90   $255.90   $255.90  
  Purchase #6 $59.84   12.577%   $67.3661   $67.37   $67.35   $67.40  
  Purchase #7 $184.50   4.545%   $192.8855   $192.89   $192.90   $192.90  
  7 purchase totals = $1,003.74       $1,070.3123   $1,070.32   $1,070.30   $1,070.40