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 $240.33   11.154%   $267.1364   $267.14   $267.15   $267.10  
  Purchase #2 $52.27   8.671%   $56.8023   $56.80   $56.80   $56.80  
  Purchase #3 $87.98   6.291%   $93.5148   $93.51   $93.50   $93.50  
  Purchase #4 $149.80   11.727%   $167.367   $167.37   $167.35   $167.40  
  Purchase #5 $202.52   3.664%   $209.9403   $209.94   $209.95   $209.90  
  Purchase #6 $230.79   10.202%   $254.3352   $254.34   $254.35   $254.30  
  Purchase #7 $15.58   13.665%   $17.709   $17.71   $17.70   $17.70  
  7 purchase totals = $979.27       $1,066.8050   $1,066.81   $1,066.80   $1,066.70