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 $63.94   11.558%   $71.3302   $71.33   $71.35   $71.30  
  Purchase #2 $200.84   5.873%   $212.6353   $212.64   $212.65   $212.60  
  Purchase #3 $250.29   10.654%   $276.9559   $276.96   $276.95   $277.00  
  Purchase #4 $57.69   8.822%   $62.7794   $62.78   $62.80   $62.80  
  Purchase #5 $16.74   8.815%   $18.2156   $18.22   $18.20   $18.20  
  Purchase #6 $129.49   9.467%   $141.7488   $141.75   $141.75   $141.70  
  Purchase #7 $38.33   10.699%   $42.4309   $42.43   $42.45   $42.40  
  7 purchase totals = $757.32       $826.0961   $826.11   $826.15   $826.00