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 $96.34   10.750%   $106.6966   $106.70   $106.70   $106.70  
  Purchase #2 $65.39   6.115%   $69.3886   $69.39   $69.40   $69.40  
  Purchase #3 $89.88   13.744%   $102.2331   $102.23   $102.25   $102.20  
  Purchase #4 $78.87   7.810%   $85.0297   $85.03   $85.05   $85.00  
  Purchase #5 $217.25   13.438%   $246.4441   $246.44   $246.45   $246.40  
  Purchase #6 $55.33   8.800%   $60.199   $60.20   $60.20   $60.20  
  Purchase #7 $113.35   11.450%   $126.3286   $126.33   $126.35   $126.30  
  7 purchase totals = $716.41       $796.3197   $796.32   $796.40   $796.20