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 $60.26   13.267%   $68.2547   $68.25   $68.25   $68.30  
  Purchase #2 $181.96   6.481%   $193.7528   $193.75   $193.75   $193.80  
  Purchase #3 $219.30   11.273%   $244.0217   $244.02   $244.00   $244.00  
  Purchase #4 $100.74   4.691%   $105.4657   $105.47   $105.45   $105.50  
  Purchase #5 $34.47   9.445%   $37.7257   $37.73   $37.75   $37.70  
  Purchase #6 $198.88   4.377%   $207.585   $207.59   $207.60   $207.60  
  Purchase #7 $113.71   4.832%   $119.2045   $119.20   $119.20   $119.20  
  7 purchase totals = $909.32       $976.0101   $976.01   $976.00   $976.10