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 $213.98   11.720%   $239.0585   $239.06   $239.05   $239.10  
  Purchase #2 $223.72   9.546%   $245.0763   $245.08   $245.10   $245.10  
  Purchase #3 $208.40   11.789%   $232.9683   $232.97   $232.95   $233.00  
  Purchase #4 $80.91   10.647%   $89.5245   $89.52   $89.50   $89.50  
  Purchase #5 $34.63   6.543%   $36.8958   $36.90   $36.90   $36.90  
  Purchase #6 $8.85   12.205%   $9.9301   $9.93   $9.95   $9.90  
  Purchase #7 $212.80   4.668%   $222.7335   $222.73   $222.75   $222.70  
  7 purchase totals = $983.29       $1,076.1870   $1,076.19   $1,076.20   $1,076.20