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 $146.91   13.534%   $166.7928   $166.79   $166.80   $166.80  
  Purchase #2 $223.92   10.539%   $247.5189   $247.52   $247.50   $247.50  
  Purchase #3 $53.40   6.434%   $56.8358   $56.84   $56.85   $56.80  
  Purchase #4 $62.45   4.148%   $65.0404   $65.04   $65.05   $65.00  
  Purchase #5 $113.71   12.770%   $128.2308   $128.23   $128.25   $128.20  
  Purchase #6 $237.29   10.826%   $262.979   $262.98   $263.00   $263.00  
  Purchase #7 $44.39   5.641%   $46.894   $46.89   $46.90   $46.90  
  7 purchase totals = $882.07       $974.2917   $974.29   $974.35   $974.20