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 $64.87   8.690%   $70.5072   $70.51   $70.50   $70.50  
  Purchase #2 $227.77   4.799%   $238.7007   $238.70   $238.70   $238.70  
  Purchase #3 $231.52   3.607%   $239.8709   $239.87   $239.85   $239.90  
  Purchase #4 $111.35   9.806%   $122.269   $122.27   $122.25   $122.30  
  Purchase #5 $220.94   11.714%   $246.8209   $246.82   $246.80   $246.80  
  Purchase #6 $148.40   11.451%   $165.3933   $165.39   $165.40   $165.40  
  Purchase #7 $237.78   12.767%   $268.1374   $268.14   $268.15   $268.10  
  7 purchase totals = $1,242.63       $1,351.6994   $1,351.70   $1,351.65   $1,351.70