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 $152.55   3.544%   $157.9564   $157.96   $157.95   $158.00  
  Purchase #2 $177.33   13.722%   $201.6632   $201.66   $201.65   $201.70  
  Purchase #3 $235.86   7.312%   $253.1061   $253.11   $253.10   $253.10  
  Purchase #4 $176.71   7.431%   $189.8413   $189.84   $189.85   $189.80  
  Purchase #5 $95.92   7.246%   $102.8704   $102.87   $102.85   $102.90  
  Purchase #6 $96.41   8.274%   $104.387   $104.39   $104.40   $104.40  
  Purchase #7 $48.81   9.245%   $53.3225   $53.32   $53.30   $53.30  
  7 purchase totals = $983.59       $1,063.1469   $1,063.15   $1,063.10   $1,063.20