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 $62.56   9.129%   $68.2711   $68.27   $68.25   $68.30  
  Purchase #2 $212.80   8.384%   $230.6412   $230.64   $230.65   $230.60  
  Purchase #3 $59.59   9.233%   $65.0919   $65.09   $65.10   $65.10  
  Purchase #4 $58.82   4.643%   $61.551   $61.55   $61.55   $61.60  
  Purchase #5 $243.25   13.775%   $276.7577   $276.76   $276.75   $276.80  
  Purchase #6 $243.72   7.829%   $262.8008   $262.80   $262.80   $262.80  
  Purchase #7 $72.79   9.650%   $79.8142   $79.81   $79.80   $79.80  
  7 purchase totals = $953.53       $1,044.9279   $1,044.92   $1,044.90   $1,045.00