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 $62.64   13.777%   $71.2699   $71.27   $71.25   $71.30  
  Purchase #2 $236.77   13.863%   $269.5934   $269.59   $269.60   $269.60  
  Purchase #3 $78.64   5.374%   $82.8661   $82.87   $82.85   $82.90  
  Purchase #4 $72.74   11.297%   $80.9574   $80.96   $80.95   $81.00  
  Purchase #5 $232.86   8.497%   $252.6461   $252.65   $252.65   $252.60  
  Purchase #6 $133.96   7.616%   $144.1624   $144.16   $144.15   $144.20  
  Purchase #7 $128.31   5.489%   $135.3529   $135.35   $135.35   $135.40  
  7 purchase totals = $945.92       $1,036.8482   $1,036.85   $1,036.80   $1,037.00