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 $187.49   13.707%   $213.1893   $213.19   $213.20   $213.20  
  Purchase #2 $209.79   5.345%   $221.0033   $221.00   $221.00   $221.00  
  Purchase #3 $23.46   5.706%   $24.7986   $24.80   $24.80   $24.80  
  Purchase #4 $152.71   12.755%   $172.1882   $172.19   $172.20   $172.20  
  Purchase #5 $70.62   7.637%   $76.0132   $76.01   $76.00   $76.00  
  Purchase #6 $249.29   11.778%   $278.6514   $278.65   $278.65   $278.70  
  Purchase #7 $156.31   6.729%   $166.8281   $166.83   $166.85   $166.80  
  7 purchase totals = $1,049.67       $1,152.6721   $1,152.67   $1,152.70   $1,152.70