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 $81.96   8.277%   $88.7438   $88.74   $88.75   $88.70  
  Purchase #2 $140.64   8.550%   $152.6647   $152.66   $152.65   $152.70  
  Purchase #3 $173.69   5.270%   $182.8435   $182.84   $182.85   $182.80  
  Purchase #4 $127.47   5.261%   $134.1762   $134.18   $134.20   $134.20  
  Purchase #5 $37.97   7.143%   $40.6822   $40.68   $40.70   $40.70  
  Purchase #6 $114.79   4.557%   $120.021   $120.02   $120.00   $120.00  
  Purchase #7 $205.53   12.677%   $231.585   $231.59   $231.60   $231.60  
  7 purchase totals = $882.05       $950.7164   $950.71   $950.75   $950.70