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 $53.39   10.252%   $58.8635   $58.86   $58.85   $58.90  
  Purchase #2 $26.88   5.341%   $28.3157   $28.32   $28.30   $28.30  
  Purchase #3 $167.44   9.805%   $183.8575   $183.86   $183.85   $183.90  
  Purchase #4 $145.42   7.517%   $156.3512   $156.35   $156.35   $156.40  
  Purchase #5 $223.43   8.249%   $241.8607   $241.86   $241.85   $241.90  
  Purchase #6 $48.99   12.204%   $54.9687   $54.97   $54.95   $55.00  
  Purchase #7 $26.70   6.465%   $28.4262   $28.43   $28.45   $28.40  
  7 purchase totals = $692.25       $752.6435   $752.65   $752.60   $752.80