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 $208.80   12.453%   $234.8019   $234.80   $234.80   $234.80  
  Purchase #2 $135.69   8.780%   $147.6036   $147.60   $147.60   $147.60  
  Purchase #3 $150.70   12.128%   $168.9769   $168.98   $169.00   $169.00  
  Purchase #4 $83.29   12.654%   $93.8295   $93.83   $93.85   $93.80  
  Purchase #5 $159.63   9.174%   $174.2745   $174.27   $174.25   $174.30  
  Purchase #6 $247.75   12.549%   $278.8401   $278.84   $278.85   $278.80  
  Purchase #7 $88.85   6.156%   $94.3196   $94.32   $94.30   $94.30  
  7 purchase totals = $1,074.71       $1,192.6461   $1,192.64   $1,192.65   $1,192.60