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 $212.44   7.226%   $227.7909   $227.79   $227.80   $227.80  
  Purchase #2 $118.30   3.265%   $122.1625   $122.16   $122.15   $122.20  
  Purchase #3 $46.55   11.546%   $51.9247   $51.92   $51.90   $51.90  
  Purchase #4 $49.33   8.643%   $53.5936   $53.59   $53.60   $53.60  
  Purchase #5 $237.52   13.598%   $269.818   $269.82   $269.80   $269.80  
  Purchase #6 $99.98   9.425%   $109.4031   $109.40   $109.40   $109.40  
  Purchase #7 $176.93   5.607%   $186.8505   $186.85   $186.85   $186.90  
  7 purchase totals = $941.05       $1,021.5433   $1,021.53   $1,021.50   $1,021.60