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 $206.65   10.257%   $227.8461   $227.85   $227.85   $227.80  
  Purchase #2 $102.73   8.165%   $111.1179   $111.12   $111.10   $111.10  
  Purchase #3 $155.91   11.227%   $173.414   $173.41   $173.40   $173.40  
  Purchase #4 $44.58   11.557%   $49.7321   $49.73   $49.75   $49.70  
  Purchase #5 $41.37   6.810%   $44.1873   $44.19   $44.20   $44.20  
  Purchase #6 $15.35   10.776%   $17.0041   $17.00   $17.00   $17.00  
  Purchase #7 $183.67   12.531%   $206.6857   $206.69   $206.70   $206.70  
  7 purchase totals = $750.26       $829.9872   $829.99   $830.00   $829.90