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 $247.76   6.249%   $263.2425   $263.24   $263.25   $263.20  
  Purchase #2 $220.84   6.741%   $235.7268   $235.73   $235.75   $235.70  
  Purchase #3 $58.44   11.568%   $65.2003   $65.20   $65.20   $65.20  
  Purchase #4 $83.72   3.671%   $86.7934   $86.79   $86.80   $86.80  
  Purchase #5 $187.89   9.207%   $205.189   $205.19   $205.20   $205.20  
  Purchase #6 $75.94   5.537%   $80.1448   $80.14   $80.15   $80.10  
  Purchase #7 $87.39   5.304%   $92.0252   $92.03   $92.05   $92.00  
  7 purchase totals = $961.98       $1,028.3220   $1,028.32   $1,028.40   $1,028.20