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 $202.97   11.122%   $225.5443   $225.54   $225.55   $225.50  
  Purchase #2 $91.88   11.643%   $102.5776   $102.58   $102.60   $102.60  
  Purchase #3 $61.86   13.317%   $70.0979   $70.10   $70.10   $70.10  
  Purchase #4 $34.32   11.596%   $38.2997   $38.30   $38.30   $38.30  
  Purchase #5 $115.37   11.554%   $128.6998   $128.70   $128.70   $128.70  
  Purchase #6 $88.74   6.451%   $94.4646   $94.46   $94.45   $94.50  
  Purchase #7 $54.61   5.173%   $57.435   $57.44   $57.45   $57.40  
  7 purchase totals = $649.75       $717.1189   $717.12   $717.15   $717.10