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 $110.37   10.802%   $122.2922   $122.29   $122.30   $122.30  
  Purchase #2 $80.80   8.570%   $87.7246   $87.72   $87.70   $87.70  
  Purchase #3 $53.87   12.558%   $60.635   $60.64   $60.65   $60.60  
  Purchase #4 $236.94   10.659%   $262.1954   $262.20   $262.20   $262.20  
  Purchase #5 $82.57   9.544%   $90.4505   $90.45   $90.45   $90.50  
  Purchase #6 $165.75   8.760%   $180.2697   $180.27   $180.25   $180.30  
  Purchase #7 $191.87   9.146%   $209.4184   $209.42   $209.40   $209.40  
  7 purchase totals = $922.17       $1,012.9858   $1,012.99   $1,012.95   $1,013.00