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 $35.92   3.543%   $37.1926   $37.19   $37.20   $37.20  
  Purchase #2 $147.87   12.709%   $166.6628   $166.66   $166.65   $166.70  
  Purchase #3 $178.77   4.169%   $186.2229   $186.22   $186.20   $186.20  
  Purchase #4 $178.29   7.420%   $191.5191   $191.52   $191.50   $191.50  
  Purchase #5 $178.46   4.454%   $186.4086   $186.41   $186.40   $186.40  
  Purchase #6 $83.28   11.310%   $92.699   $92.70   $92.70   $92.70  
  Purchase #7 $93.26   8.507%   $101.1936   $101.19   $101.20   $101.20  
  7 purchase totals = $895.85       $961.8986   $961.89   $961.85   $961.90