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 $60.52   5.405%   $63.7911   $63.79   $63.80   $63.80  
  Purchase #2 $172.97   12.125%   $193.9426   $193.94   $193.95   $193.90  
  Purchase #3 $66.71   9.704%   $73.1835   $73.18   $73.20   $73.20  
  Purchase #4 $165.80   13.539%   $188.2477   $188.25   $188.25   $188.20  
  Purchase #5 $89.92   5.535%   $94.8971   $94.90   $94.90   $94.90  
  Purchase #6 $186.70   10.512%   $206.3259   $206.33   $206.35   $206.30  
  Purchase #7 $141.25   7.197%   $151.4158   $151.42   $151.40   $151.40  
  7 purchase totals = $883.87       $971.8037   $971.81   $971.85   $971.70