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 $165.96   6.207%   $176.2611   $176.26   $176.25   $176.30  
  Purchase #2 $181.57   3.503%   $187.9304   $187.93   $187.95   $187.90  
  Purchase #3 $64.44   11.607%   $71.9196   $71.92   $71.90   $71.90  
  Purchase #4 $23.65   10.640%   $26.1664   $26.17   $26.15   $26.20  
  Purchase #5 $82.35   6.639%   $87.8172   $87.82   $87.80   $87.80  
  Purchase #6 $216.56   3.418%   $223.962   $223.96   $223.95   $224.00  
  Purchase #7 $224.81   7.843%   $242.4418   $242.44   $242.45   $242.40  
  7 purchase totals = $959.34       $1,016.4985   $1,016.50   $1,016.45   $1,016.50