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 $170.27   3.764%   $176.679   $176.68   $176.70   $176.70  
  Purchase #2 $165.75   13.263%   $187.7334   $187.73   $187.75   $187.70  
  Purchase #3 $32.51   13.860%   $37.0159   $37.02   $37.00   $37.00  
  Purchase #4 $169.87   12.583%   $191.2447   $191.24   $191.25   $191.20  
  Purchase #5 $97.74   9.464%   $106.9901   $106.99   $107.00   $107.00  
  Purchase #6 $226.53   13.364%   $256.8035   $256.80   $256.80   $256.80  
  Purchase #7 $54.37   10.866%   $60.2778   $60.28   $60.30   $60.30  
  7 purchase totals = $917.04       $1,016.7444   $1,016.74   $1,016.80   $1,016.70