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 $92.85   11.554%   $103.5779   $103.58   $103.60   $103.60  
  Purchase #2 $79.80   5.715%   $84.3606   $84.36   $84.35   $84.40  
  Purchase #3 $24.53   9.588%   $26.8819   $26.88   $26.90   $26.90  
  Purchase #4 $163.96   8.363%   $177.672   $177.67   $177.65   $177.70  
  Purchase #5 $245.92   10.171%   $270.9325   $270.93   $270.95   $270.90  
  Purchase #6 $52.68   13.150%   $59.6074   $59.61   $59.60   $59.60  
  Purchase #7 $10.40   9.162%   $11.3528   $11.35   $11.35   $11.40  
  7 purchase totals = $670.14       $734.3851   $734.38   $734.40   $734.50