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 $125.77   13.194%   $142.3641   $142.36   $142.35   $142.40  
  Purchase #2 $177.48   11.464%   $197.8263   $197.83   $197.85   $197.80  
  Purchase #3 $184.85   7.452%   $198.625   $198.63   $198.65   $198.60  
  Purchase #4 $181.40   3.829%   $188.3458   $188.35   $188.35   $188.30  
  Purchase #5 $5.46   11.443%   $6.0848   $6.08   $6.10   $6.10  
  Purchase #6 $48.58   7.826%   $52.3819   $52.38   $52.40   $52.40  
  Purchase #7 $224.29   7.132%   $240.2864   $240.29   $240.30   $240.30  
  7 purchase totals = $947.83       $1,025.9143   $1,025.92   $1,026.00   $1,025.90