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 $166.96   10.195%   $183.9816   $183.98   $184.00   $184.00  
  Purchase #2 $187.73   7.724%   $202.2303   $202.23   $202.25   $202.20  
  Purchase #3 $245.29   6.511%   $261.2608   $261.26   $261.25   $261.30  
  Purchase #4 $218.49   5.132%   $229.7029   $229.70   $229.70   $229.70  
  Purchase #5 $61.97   9.405%   $67.7983   $67.80   $67.80   $67.80  
  Purchase #6 $231.74   12.679%   $261.1223   $261.12   $261.10   $261.10  
  Purchase #7 $34.96   9.275%   $38.2025   $38.20   $38.20   $38.20  
  7 purchase totals = $1,147.14       $1,244.2987   $1,244.29   $1,244.30   $1,244.30