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 $236.67   13.183%   $267.8702   $267.87   $267.85   $267.90  
  Purchase #2 $60.56   8.436%   $65.6688   $65.67   $65.65   $65.70  
  Purchase #3 $239.64   12.232%   $268.9528   $268.95   $268.95   $269.00  
  Purchase #4 $241.74   11.206%   $268.8294   $268.83   $268.85   $268.80  
  Purchase #5 $205.94   11.705%   $230.0453   $230.05   $230.05   $230.00  
  Purchase #6 $10.79   3.177%   $11.1328   $11.13   $11.15   $11.10  
  Purchase #7 $93.80   6.433%   $99.8342   $99.83   $99.85   $99.80  
  7 purchase totals = $1,089.14       $1,212.3335   $1,212.33   $1,212.35   $1,212.30