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 $207.78   7.722%   $223.8248   $223.82   $223.80   $223.80  
  Purchase #2 $62.58   6.107%   $66.4018   $66.40   $66.40   $66.40  
  Purchase #3 $108.47   8.391%   $117.5717   $117.57   $117.55   $117.60  
  Purchase #4 $200.57   5.279%   $211.1581   $211.16   $211.15   $211.20  
  Purchase #5 $178.31   10.693%   $197.3767   $197.38   $197.40   $197.40  
  Purchase #6 $235.96   12.763%   $266.0756   $266.08   $266.10   $266.10  
  Purchase #7 $174.29   5.800%   $184.3988   $184.40   $184.40   $184.40  
  7 purchase totals = $1,167.96       $1,266.8075   $1,266.81   $1,266.80   $1,266.90