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 $113.65   10.834%   $125.9628   $125.96   $125.95   $126.00  
  Purchase #2 $16.74   5.252%   $17.6192   $17.62   $17.60   $17.60  
  Purchase #3 $196.71   12.721%   $221.7335   $221.73   $221.75   $221.70  
  Purchase #4 $69.69   4.415%   $72.7668   $72.77   $72.75   $72.80  
  Purchase #5 $156.96   7.682%   $169.0177   $169.02   $169.00   $169.00  
  Purchase #6 $68.53   5.736%   $72.4609   $72.46   $72.45   $72.50  
  Purchase #7 $198.73   6.535%   $211.717   $211.72   $211.70   $211.70  
  7 purchase totals = $821.01       $891.2779   $891.28   $891.20   $891.30