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 $67.38   5.541%   $71.1135   $71.11   $71.10   $71.10  
  Purchase #2 $34.54   10.182%   $38.0569   $38.06   $38.05   $38.10  
  Purchase #3 $167.70   11.545%   $187.061   $187.06   $187.05   $187.10  
  Purchase #4 $226.32   9.426%   $247.6529   $247.65   $247.65   $247.70  
  Purchase #5 $243.87   11.340%   $271.5249   $271.52   $271.50   $271.50  
  Purchase #6 $212.28   6.280%   $225.6112   $225.61   $225.60   $225.60  
  Purchase #7 $27.75   9.285%   $30.3266   $30.33   $30.35   $30.30  
  7 purchase totals = $979.84       $1,071.3470   $1,071.34   $1,071.30   $1,071.40