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 $117.95   3.663%   $122.2705   $122.27   $122.25   $122.30  
  Purchase #2 $240.27   6.153%   $255.0538   $255.05   $255.05   $255.10  
  Purchase #3 $174.83   5.255%   $184.0173   $184.02   $184.00   $184.00  
  Purchase #4 $57.40   8.655%   $62.368   $62.37   $62.35   $62.40  
  Purchase #5 $215.82   9.396%   $236.0984   $236.10   $236.10   $236.10  
  Purchase #6 $132.98   3.668%   $137.8577   $137.86   $137.85   $137.90  
  Purchase #7 $22.31   3.435%   $23.0763   $23.08   $23.10   $23.10  
  7 purchase totals = $961.56       $1,020.7420   $1,020.75   $1,020.70   $1,020.90