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 $247.69   11.564%   $276.3329   $276.33   $276.35   $276.30  
  Purchase #2 $84.57   12.391%   $95.0491   $95.05   $95.05   $95.00  
  Purchase #3 $153.79   3.438%   $159.0773   $159.08   $159.10   $159.10  
  Purchase #4 $199.98   5.110%   $210.199   $210.20   $210.20   $210.20  
  Purchase #5 $63.45   7.431%   $68.165   $68.17   $68.15   $68.20  
  Purchase #6 $196.86   13.418%   $223.2747   $223.27   $223.25   $223.30  
  Purchase #7 $213.34   8.580%   $231.6446   $231.64   $231.65   $231.60  
  7 purchase totals = $1,159.68       $1,263.7426   $1,263.74   $1,263.75   $1,263.70