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 $158.73   4.388%   $165.6951   $165.70   $165.70   $165.70  
  Purchase #2 $243.52   3.660%   $252.4328   $252.43   $252.45   $252.40  
  Purchase #3 $129.86   12.303%   $145.8367   $145.84   $145.85   $145.80  
  Purchase #4 $230.74   5.270%   $242.9   $242.90   $242.90   $242.90  
  Purchase #5 $134.88   11.631%   $150.5679   $150.57   $150.55   $150.60  
  Purchase #6 $60.96   10.852%   $67.5754   $67.58   $67.60   $67.60  
  Purchase #7 $207.55   8.224%   $224.6189   $224.62   $224.60   $224.60  
  7 purchase totals = $1,166.24       $1,249.6268   $1,249.64   $1,249.65   $1,249.60