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 $85.82   13.214%   $97.1603   $97.16   $97.15   $97.20  
  Purchase #2 $179.46   4.115%   $186.8448   $186.84   $186.85   $186.80  
  Purchase #3 $141.86   5.562%   $149.7503   $149.75   $149.75   $149.80  
  Purchase #4 $80.74   3.864%   $83.8598   $83.86   $83.85   $83.90  
  Purchase #5 $120.46   3.701%   $124.9182   $124.92   $124.90   $124.90  
  Purchase #6 $210.54   6.696%   $224.6378   $224.64   $224.65   $224.60  
  Purchase #7 $67.48   4.245%   $70.3445   $70.34   $70.35   $70.30  
  7 purchase totals = $886.36       $937.5157   $937.51   $937.50   $937.50