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 $67.86   8.303%   $73.4944   $73.49   $73.50   $73.50  
  Purchase #2 $100.96   7.563%   $108.5956   $108.60   $108.60   $108.60  
  Purchase #3 $187.59   7.751%   $202.1301   $202.13   $202.15   $202.10  
  Purchase #4 $84.91   4.843%   $89.0222   $89.02   $89.00   $89.00  
  Purchase #5 $35.54   12.836%   $40.1019   $40.10   $40.10   $40.10  
  Purchase #6 $235.90   4.573%   $246.6877   $246.69   $246.70   $246.70  
  Purchase #7 $142.45   6.434%   $151.6152   $151.62   $151.60   $151.60  
  7 purchase totals = $855.21       $911.6471   $911.65   $911.65   $911.60