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 $226.27   4.153%   $235.667   $235.67   $235.65   $235.70  
  Purchase #2 $213.68   6.671%   $227.9346   $227.93   $227.95   $227.90  
  Purchase #3 $66.71   3.188%   $68.8367   $68.84   $68.85   $68.80  
  Purchase #4 $48.55   13.445%   $55.0775   $55.08   $55.10   $55.10  
  Purchase #5 $230.90   12.551%   $259.8803   $259.88   $259.90   $259.90  
  Purchase #6 $49.58   5.490%   $52.3019   $52.30   $52.30   $52.30  
  Purchase #7 $85.57   10.227%   $94.3212   $94.32   $94.30   $94.30  
  7 purchase totals = $921.26       $994.0192   $994.02   $994.05   $994.00