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 $59.37   3.115%   $61.2194   $61.22   $61.20   $61.20  
  Purchase #2 $120.88   11.499%   $134.78   $134.78   $134.80   $134.80  
  Purchase #3 $48.81   5.619%   $51.5526   $51.55   $51.55   $51.60  
  Purchase #4 $187.55   11.272%   $208.6906   $208.69   $208.70   $208.70  
  Purchase #5 $62.36   12.706%   $70.2835   $70.28   $70.30   $70.30  
  Purchase #6 $156.99   5.729%   $165.984   $165.98   $166.00   $166.00  
  Purchase #7 $209.29   11.180%   $232.6886   $232.69   $232.70   $232.70  
  7 purchase totals = $845.25       $925.1987   $925.19   $925.25   $925.30