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 $206.29   8.275%   $223.3605   $223.36   $223.35   $223.40  
  Purchase #2 $166.99   8.711%   $181.5365   $181.54   $181.55   $181.50  
  Purchase #3 $18.31   3.856%   $19.016   $19.02   $19.00   $19.00  
  Purchase #4 $58.44   13.290%   $66.2067   $66.21   $66.20   $66.20  
  Purchase #5 $81.44   12.175%   $91.3553   $91.36   $91.35   $91.40  
  Purchase #6 $213.74   13.667%   $242.9518   $242.95   $242.95   $243.00  
  Purchase #7 $198.62   6.733%   $211.9931   $211.99   $212.00   $212.00  
  7 purchase totals = $943.83       $1,036.4199   $1,036.43   $1,036.40   $1,036.50