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 $245.89   5.336%   $259.0107   $259.01   $259.00   $259.00  
  Purchase #2 $135.42   11.734%   $151.3102   $151.31   $151.30   $151.30  
  Purchase #3 $119.86   5.678%   $126.6657   $126.67   $126.65   $126.70  
  Purchase #4 $107.36   6.178%   $113.9927   $113.99   $114.00   $114.00  
  Purchase #5 $24.32   4.164%   $25.3327   $25.33   $25.35   $25.30  
  Purchase #6 $28.26   11.524%   $31.5167   $31.52   $31.50   $31.50  
  Purchase #7 $182.69   9.369%   $199.8062   $199.81   $199.80   $199.80  
  7 purchase totals = $843.80       $907.6349   $907.64   $907.60   $907.60