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 $208.88   8.518%   $226.6724   $226.67   $226.65   $226.70  
  Purchase #2 $30.68   4.327%   $32.0075   $32.01   $32.00   $32.00  
  Purchase #3 $156.28   4.650%   $163.547   $163.55   $163.55   $163.50  
  Purchase #4 $69.36   9.346%   $75.8424   $75.84   $75.85   $75.80  
  Purchase #5 $184.53   13.228%   $208.9396   $208.94   $208.95   $208.90  
  Purchase #6 $150.90   4.439%   $157.5985   $157.60   $157.60   $157.60  
  Purchase #7 $222.93   9.575%   $244.2755   $244.28   $244.30   $244.30  
  7 purchase totals = $1,023.56       $1,108.8829   $1,108.89   $1,108.90   $1,108.80