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 $131.71   11.273%   $146.5577   $146.56   $146.55   $146.60  
  Purchase #2 $246.70   10.483%   $272.5616   $272.56   $272.55   $272.60  
  Purchase #3 $145.53   8.125%   $157.3543   $157.35   $157.35   $157.40  
  Purchase #4 $88.87   10.821%   $98.4866   $98.49   $98.50   $98.50  
  Purchase #5 $11.54   13.815%   $13.1343   $13.13   $13.15   $13.10  
  Purchase #6 $241.33   8.850%   $262.6877   $262.69   $262.70   $262.70  
  Purchase #7 $41.33   7.771%   $44.5418   $44.54   $44.55   $44.50  
  7 purchase totals = $907.01       $995.3240   $995.32   $995.35   $995.40