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 $90.68   6.626%   $96.6885   $96.69   $96.70   $96.70  
  Purchase #2 $159.50   10.192%   $175.7562   $175.76   $175.75   $175.80  
  Purchase #3 $206.90   13.199%   $234.2087   $234.21   $234.20   $234.20  
  Purchase #4 $87.80   10.500%   $97.019   $97.02   $97.00   $97.00  
  Purchase #5 $5.37   11.573%   $5.9915   $5.99   $6.00   $6.00  
  Purchase #6 $109.25   10.721%   $120.9627   $120.96   $120.95   $121.00  
  Purchase #7 $87.48   7.477%   $94.0209   $94.02   $94.00   $94.00  
  7 purchase totals = $746.98       $824.6475   $824.65   $824.60   $824.70