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 $59.60   5.524%   $62.8923   $62.89   $62.90   $62.90  
  Purchase #2 $188.85   7.343%   $202.7173   $202.72   $202.70   $202.70  
  Purchase #3 $225.35   13.183%   $255.0579   $255.06   $255.05   $255.10  
  Purchase #4 $73.99   12.626%   $83.332   $83.33   $83.35   $83.30  
  Purchase #5 $27.54   4.241%   $28.708   $28.71   $28.70   $28.70  
  Purchase #6 $29.62   12.118%   $33.2094   $33.21   $33.20   $33.20  
  Purchase #7 $59.32   7.222%   $63.6041   $63.60   $63.60   $63.60  
  7 purchase totals = $664.27       $729.5210   $729.52   $729.50   $729.50