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 $201.25   13.721%   $228.8635   $228.86   $228.85   $228.90  
  Purchase #2 $164.50   13.121%   $186.084   $186.08   $186.10   $186.10  
  Purchase #3 $87.38   9.820%   $95.9607   $95.96   $95.95   $96.00  
  Purchase #4 $101.27   5.154%   $106.4895   $106.49   $106.50   $106.50  
  Purchase #5 $220.56   9.854%   $242.294   $242.29   $242.30   $242.30  
  Purchase #6 $30.64   3.336%   $31.6622   $31.66   $31.65   $31.70  
  Purchase #7 $108.67   11.597%   $121.2725   $121.27   $121.25   $121.30  
  7 purchase totals = $914.27       $1,012.6264   $1,012.61   $1,012.60   $1,012.80