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 $171.27   7.508%   $184.129   $184.13   $184.15   $184.10  
  Purchase #2 $224.52   10.773%   $248.7075   $248.71   $248.70   $248.70  
  Purchase #3 $84.73   6.358%   $90.1171   $90.12   $90.10   $90.10  
  Purchase #4 $191.77   5.856%   $203.0001   $203.00   $203.00   $203.00  
  Purchase #5 $168.85   7.871%   $182.1402   $182.14   $182.15   $182.10  
  Purchase #6 $95.38   4.415%   $99.591   $99.59   $99.60   $99.60  
  Purchase #7 $23.61   13.292%   $26.7482   $26.75   $26.75   $26.70  
  7 purchase totals = $960.13       $1,034.4331   $1,034.44   $1,034.45   $1,034.30