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 $200.97   12.848%   $226.7906   $226.79   $226.80   $226.80  
  Purchase #2 $132.58   6.382%   $141.0413   $141.04   $141.05   $141.00  
  Purchase #3 $33.54   7.825%   $36.1645   $36.16   $36.15   $36.20  
  Purchase #4 $110.40   6.444%   $117.5142   $117.51   $117.50   $117.50  
  Purchase #5 $132.59   7.511%   $142.5488   $142.55   $142.55   $142.50  
  Purchase #6 $237.29   3.651%   $245.9535   $245.95   $245.95   $246.00  
  Purchase #7 $104.70   6.708%   $111.7233   $111.72   $111.70   $111.70  
  7 purchase totals = $952.07       $1,021.7362   $1,021.72   $1,021.70   $1,021.70