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 $57.94   8.118%   $62.6436   $62.64   $62.65   $62.60  
  Purchase #2 $24.76   3.682%   $25.6717   $25.67   $25.65   $25.70  
  Purchase #3 $131.98   9.107%   $143.9994   $144.00   $144.00   $144.00  
  Purchase #4 $41.96   9.275%   $45.8518   $45.85   $45.85   $45.90  
  Purchase #5 $172.90   12.381%   $194.3067   $194.31   $194.30   $194.30  
  Purchase #6 $172.63   7.536%   $185.6394   $185.64   $185.65   $185.60  
  Purchase #7 $73.74   13.832%   $83.9397   $83.94   $83.95   $83.90  
  7 purchase totals = $675.91       $742.0523   $742.05   $742.05   $742.00