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 $50.47   4.568%   $52.7755   $52.78   $52.80   $52.80  
  Purchase #2 $234.91   3.703%   $243.6087   $243.61   $243.60   $243.60  
  Purchase #3 $19.99   13.319%   $22.6525   $22.65   $22.65   $22.70  
  Purchase #4 $144.43   10.320%   $159.3352   $159.34   $159.35   $159.30  
  Purchase #5 $209.99   7.252%   $225.2185   $225.22   $225.20   $225.20  
  Purchase #6 $194.77   10.359%   $214.9462   $214.95   $214.95   $214.90  
  Purchase #7 $96.52   12.372%   $108.4615   $108.46   $108.45   $108.50  
  7 purchase totals = $951.08       $1,026.9981   $1,027.01   $1,027.00   $1,027.00