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 $61.45   3.456%   $63.5737   $63.57   $63.55   $63.60  
  Purchase #2 $49.94   12.623%   $56.2439   $56.24   $56.25   $56.20  
  Purchase #3 $177.74   8.788%   $193.3598   $193.36   $193.35   $193.40  
  Purchase #4 $66.60   7.289%   $71.4545   $71.45   $71.45   $71.50  
  Purchase #5 $24.86   7.205%   $26.6512   $26.65   $26.65   $26.70  
  Purchase #6 $204.82   12.211%   $229.8306   $229.83   $229.85   $229.80  
  Purchase #7 $223.41   9.648%   $244.9646   $244.96   $244.95   $245.00  
  7 purchase totals = $808.82       $886.0783   $886.06   $886.05   $886.20