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 $223.67   13.150%   $253.0826   $253.08   $253.10   $253.10  
  Purchase #2 $127.58   11.775%   $142.6025   $142.60   $142.60   $142.60  
  Purchase #3 $71.28   13.266%   $80.736   $80.74   $80.75   $80.70  
  Purchase #4 $29.37   13.291%   $33.2736   $33.27   $33.25   $33.30  
  Purchase #5 $198.88   6.284%   $211.3776   $211.38   $211.40   $211.40  
  Purchase #6 $245.77   8.725%   $267.2134   $267.21   $267.20   $267.20  
  Purchase #7 $165.72   4.394%   $173.0017   $173.00   $173.00   $173.00  
  7 purchase totals = $1,062.27       $1,161.2874   $1,161.28   $1,161.30   $1,161.30