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 $232.55   10.537%   $257.0538   $257.05   $257.05   $257.10  
  Purchase #2 $23.60   10.179%   $26.0022   $26.00   $26.00   $26.00  
  Purchase #3 $122.95   4.533%   $128.5233   $128.52   $128.50   $128.50  
  Purchase #4 $69.79   6.372%   $74.237   $74.24   $74.25   $74.20  
  Purchase #5 $239.43   6.321%   $254.5644   $254.56   $254.55   $254.60  
  Purchase #6 $185.35   13.613%   $210.5817   $210.58   $210.60   $210.60  
  Purchase #7 $161.74   7.588%   $174.0128   $174.01   $174.00   $174.00  
  7 purchase totals = $1,035.41       $1,124.9752   $1,124.96   $1,124.95   $1,125.00